[p. 115] WILKINS, Justice.

 David and Ginger Twitchell appeal from their convictions of involuntary manslaughter in connection with the April 8, 1986, death of their two and one- half year old son Robyn. Robyn died of the consequences of peritonitis caused by the perforation of his bowel which had been obstructed as a result of an anomaly known as Meckel's diverticulum.  There was evidence that the condition could be corrected by surgery with a high success rate.

 The defendants are practicing Christian Scientists who grew up in Christian Science families.  They believe in healing by spiritual treatment.  During Robyn's five-day illness from Friday, April 4, through Tuesday, April 8, they retained a Christian Science practitioner, a Christian Science nurse, and at one time consulted with Nathan Talbot, who held a position in the church known as the "Committee on Publication." [n. 3]  As a result of that consultation, David Twitchell read a church publication concerning the legal rights and obligations of Christian Scientists in Massachusetts.  That publication quoted a portion of G.L. c. 273, § 1, as then amended, which, at least in the context of the crimes described [p. 116] in that section, accepted remedial treatment by spiritual means alone as satisfying any parental obligation not to neglect a child or to provide a child with physical care.  We shall subsequently discuss this statute in connection with the defendants' claim, rejected by the trial judge, that the spiritual treatment provision in G.L. c. 273, § 1, protects them from criminal liability for manslaughter. [n. 4]
 

3. The "Committee on Publication" for each State is a one-person committee authorized by the church's founder, Mary Baker Eddy, to explain Christian Science to the community and to give advice to practitioners. Talbot was head of all the Committees on Publication in the country.

4. The spiritual treatment provision then read, as it does now, as follows:  "A child shall not be deemed to be neglected or lack proper physical care for the sole reason that he is being provided remedial treatment by spiritual means alone in accordance with the tenets and practice of a recognized church or religious denomination by a duly accredited practitioner thereof."  G.L. c. 273, § 1 (1992 ed.).

 We need not recite in detail the circumstances of Robyn's illness.  The jury would have been warranted in concluding that Robyn was in considerable distress and that, in the absence of their belief in and reliance on spiritual treatment, the parents of a child in his condition would normally have sought medical treatment in sufficient time to save that child's life.  There was also evidence that the intensity of Robyn's distress ebbed and flowed, perhaps causing his parents to believe that prayer would lead to the healing of the illness.  On the other hand, the jury would have been warranted in finding that the Twitchells were wanton or reckless in failing to provide medical care for Robyn, if parents have a legal duty to provide a child with medical care in such circumstances and if the spiritual treatment provision of G.L. c. 273, § 1, did not protect them from manslaughter liability.

 We shall conclude that parents have a duty to seek medical attention for a child in Robyn's circumstances, the violation of which, if their conduct was wanton or reckless, could support a conviction of involuntary manslaughter and that the spiritual healing provision in G.L. c. 273, § 1, did not bar a prosecution for manslaughter in these circumstances.  We further conclude, however, that special circumstances in this case would justify a jury's finding that the Twitchells reasonably believed that they could rely on spiritual treatment [p. 117] without fear of criminal prosecution.  This affirmative defense should have been asserted and presented to the jury. Because it was not, there is a substantial risk of a miscarriage of justice in this case, and, therefore, the judgments must be reversed.

 1. We shall first consider whether the law generally imposes a parental duty to provide medical services to a child, the breach of which can be the basis of a conviction for involuntary manslaughter.  We thus put aside temporarily the question of what, if any, application the spiritual treatment provision in G.L. c. 273, § 1, has to this case.

 The Commonwealth presented its case on the theory that each defendant was guilty of involuntary manslaughter because the intentional failure of each to seek medical attention for their son involved such "a high degree of likelihood that substantial harm will result to" him as to be wanton or reckless conduct.  Commonwealth v. Welansky, 316 Mass. 383, 399, 55 N.E.2d 902 (1944).  See Commonwealth v. Godin, 374 Mass. 120, 129, 371 N.E.2d 438 (1977), cert. denied, 436 U.S. 917, 98 S.Ct. 2263, 56 L.Ed.2d 758 (1978).  Our definition of involuntary manslaughter derives from the common law.  See Commonwealth v. Catalina, 407 Mass. 779, 783, 556 N.E.2d 973 (1990).  A charge of involuntary manslaughter based on an omission to act can be proved only if the defendant had a duty to act and did not do so. Commonwealth v. Welansky, supra.  That duty, however, is not limited to those duties whose violation would create civil liability.  Commonwealth v. Godin, supra 374 Mass. at 126-127, 371 N.E.2d 438.

 The Commonwealth claims that the defendants owed an affirmative duty of care to their son which they wantonly or recklessly failed to perform. The duty to provide sufficient support for a child is legally enforceable in a civil proceeding against a parent.  See Ventura v. Ventura, 407 Mass. 724, 729, 555 N.E.2d 872 (1990).  A breach of that duty is a misdemeanor.  G.L. c. 273, § 1 (1992 ed.).  Where necessary to protect a child's well-being, the Commonwealth may intervene, over the parents' objections, to assure that needed services are provided.  See Matter of McCauley, 409 Mass. 134, 137, 565 N.E.2d 411 (1991);  Custody of a Minor, 375 Mass. 733, 748-749, 379 N.E.2d 1053 (1978).  More important, [p. 118] for our current purposes, a parental duty of care has been recognized in the common law of homicide in this Commonwealth.  See Commonwealth v. Hall, 322 Mass. 523, 528, 78 N.E.2d 644 (1948) (conviction of murder in the second degree based on withholding of food and liquids).

 . . . . There is [also], quite apart from § 1, a common law duty to provide medical services for a child, the breach of which can be the basis, in the appropriate circumstances, for the conviction of a parent for involuntary manslaughter.

 2. We, therefore, consider the impact, if any, of G.L. c. 273, § 1, on this case.  The defendants argue that the spiritual treatment provision in § 1 bars any involuntary manslaughter charge against a parent who relies, as they did, on spiritual treatment and who does not seek medical attention for his or her child, even if the parent's failure to seek such [p. 119] care would otherwise be wanton or reckless conduct.  We disagree.

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 [p. 120] Section 1 of G.L. c. 273 provides no complete protection to a parent against a charge of involuntary manslaughter that is based on the parent's wanton or reckless failure to provide medical services to a child. [n. 6]  Section 1 concerns child support and care in a chapter of the General Laws that deals not so much with the punishment of criminal conduct as with motivating parents to fulfil their natural obligations of support.  See Kelley, petitioner, 292 Mass. 198, 200, 197 N.E. 861 (1935); Commonwealth v. Herrick, 263 Mass. 25, 26, 160 N.E. 531 (1928); Commonwealth v. Acker, 197 Mass. 91, 92-93, 83 N.E. 312 (1908).  On the other hand, the principle underlying involuntary manslaughter is the Commonwealth's "interest that persons within its territory should not be killed by the wanton and reckless conduct of others."  Commonwealth v. Godin, 374 Mass. 120, 126, 371 N.E.2d 438 (1977).  See Commonwealth v. Atencio, 345 Mass. 627, 629, 189 N.E.2d 223 (1963).  It is unlikely that the Legislature placed the spiritual treatment provision in § 1 to provide a defense to, [p. 121] or to alter any definition of, common law homicide. [n. 7]  There is no history to § 1 that suggests that the spiritual treatment provision carries any message beyond § 1 itself. [n. 8]  The act that added the spiritual treatment provision was entitled "An Act defining the term 'proper physical care' under the law relative to care of children by a parent."  St.1971, c. 762.  The amendment's concern seems focused on the subject matter of § 1 and certainly not directed toward changing the common law of homicide.  Indeed, that was the view expressed at the time by a representative of the Christian Science Church. [n. 9]
 

6. At the time of Robyn Twitchell's death, the relevant parts of G.L.  c. 273, § 1, read as follows:
"Any spouse or parent who without just cause deserts his spouse or minor child, whether by going into another town in the commonwealth or into another state, and leaves them or any or either of them without making reasonable provision for their support, and any spouse or parent who unreasonably neglects or refuses to provide for the support and maintenance of his spouse, whether living with him or living apart from him for justifiable cause, or of his minor child, and any spouse or parent who abandons or leaves his spouse or minor child in danger of becoming a burden upon the public, and any parent of a minor child or any guardian with care and custody of a minor child, or any custodian of a minor child, who willfully fails to provide necessary and proper physical, educational or moral care and guidance, or who permits said child to grow up under conditions or circumstances damaging to the child's sound character development, or who fails to provide proper attention for said child, shall be punished by a fine of not more than five hundred dollars or by imprisonment for not more than two years, or both.  A child shall not be deemed to be neglected or lack proper physical care for the sole reason that he is being provided remedial treatment by spiritual means alone in accordance with the tenets and practice of a recognized church or religious denomination by a duly accredited practitioner thereof."  G.L. c. 273, § 1, as appearing in St.1977, c. 848, § 2.

7. General Laws c. 265, § 13 (1992 ed.), which fixes the penalty for common law manslaughter, would be the logical place for any such recognition of spiritual treatment as barring a charge of involuntary manslaughter.

8. A predecessor of § 1, enacted in 1882, provided that "[w]hoever unreasonably neglects to provide for the support of his minor child shall be punished by fine ... or by imprisonment."  St.1882, c. 270, § 4.  After several minor amendments, the statute was rewritten in 1909 to impose, among other things, a duty of physical care of children on parents:  "[A]ny parent ... whose minor child, by reason of the neglect, cruelty, drunkenness, habits of crime, or other vice of such parent, is growing up ... without proper physical care ... shall be punished."  St.1909, c. 180.  This formulation survived major revisions in 1911 and 1931.  See St.1911, c. 456, § 1;  St.1931, c. 226.  In 1954, G.L. c. 273, § 1, was amended to state that "any parent of a minor child ... who wilfully fails to provide necessary and proper physical, educational or moral care and guidance ... shall be punished."  St.1954, c. 539.  The spiritual treatment provision was added in 1971.  St.1971, c. 762.  With minor  revisions making § 1 gender-neutral (St.1977, c. 848, § 2), this is how § 1 stood at the time of Robyn Twitchell's death.  See note 6 above.
Section 1 was rewritten by St.1986, c. 310, § 22.  The amendment removed from § 1 any reference to wilful failure to provide necessary and proper physical care and limited any violation of § 1 to matters of failure to support.  Nevertheless, the spiritual treatment language with which we are here concerned was retained verbatim, even though that portion of it that concerns the lack of proper physical care no longer seems applicable to any crime defined in § 1.  See St.1986, c. 310, § 22.  It is arguable that, because of the 1986 amendment, the spiritual treatment provision of § 1 has an application outside of § 1 that it did not have before.  The Legislature may wish to consider ways by which the new uncertainty can be resolved.

9. A statement was made to a legislative committee in February, 1971, by Dr. J. Buroughs Stokes, the then "Committee on Publication for The First Church of Christ, Scientist."  That statement is available in the archives concerning St.1971, c. 762.  It indicates that the Christian Science Church had proposed an amendment to G.L. c. 273, § 1, "to make it clear that Christian Scientists, in providing their children with Christian Science treatment and care, are not violating this law" (emphasis supplied).  Id. at 2.  "We are seeking legal protection from the possibility of being considered neglectful by any individual in authority who may misunderstand our methods...."  Id. at 3.

 [p. 122] The spiritual treatment provision refers to neglect and lack of proper physical care, which are concepts set forth earlier in § 1, as then amended, as bases for punishment:  (1) neglect to provide support and (2) wilful failure to provide necessary and proper physical care. These concepts do not underlie involuntary manslaughter.  Wanton or reckless conduct is not a form of negligence.  See Commonwealth v. Godin, supra 374 Mass. at 127, 371 N.E.2d 438.  Wanton or reckless conduct does not involve a wilful intention to cause the resulting harm.  See Commonwealth v. Welansky, 316 Mass. 383, 397-398, 55 N.E.2d 902 (1944).  An involuntary manslaughter verdict does not require proof of wilfulness.  See Commonwealth v. Catalina, 407 Mass. 779, 789, 556 N.E.2d 973 (1990);  Commonwealth v. Welansky, supra 316 Mass. at 397-398, 399, 55 N.E.2d 902.  Thus, by its terms, the spiritual treatment provision in § 1 does not apply to involuntary manslaughter.

 [p. 123] 3. The defendants argue that the failure to extend the protection of the spiritual treatment provision to them in this case would be a denial of due process of law because they lacked "fair warning" that their use of spiritual treatment could form the basis for a prosecution for manslaughter. Fair warning is part of the due process doctrine of vagueness, which "requires that a penal statute define the criminal offense with sufficient definiteness that ordinary people can understand what conduct is prohibited and in a manner that does not encourage arbitrary and discriminatory enforcement."  . . . . Even if a statute is clear on its face, there may not be fair warning in the circumstances of particular defendants.  The defendants here argue that they have been denied fair warning . . . because they were officially misled by an opinion of the Attorney General of the Commonwealth [p. 124] (Raley v. Ohio, 360 U.S. 423, 438-439, 79 S.Ct. 1257, 1266-1267, 3 L.Ed.2d 1344 [1959];  United States v. Pennsylvania Indus. Chem. Corp., 411 U.S. 655, 674-675, 93 S.Ct. 1804, 1816-1817, 36 L.Ed.2d 567 [1973] ).  We find some merit only in the last of these contentions.

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 [p. 126] In May, 1975, the Attorney General gave an opinion on a number of topics to the deputy director of the Office for Children.  Rep. A.G., Pub.Doc. No. 12, at 139 (1975).  The relevant portion of that opinion, which is quoted in the margin, [n. 15] answers a general question "whether parents who fail to provide medical services to children on the basis of religious beliefs will be subject to prosecution for such failure."  Id. at 140.  A reasonable person not trained in the law might fairly read the Attorney General's comments as being a negative answer to the general question whether in any circumstances such parents may be prosecuted.  It is true that the answer comes to focus on negligent failures of parents, and we know that wanton or reckless failures are different.  But an answer that says that children may receive needed services "[p. 127] notwithstanding the inability to prosecute parents in such cases" (id.), and issues no caveat concerning homicide charges, invites a conclusion that parents who fail to provide medical services to children on the basis of religious beliefs are not subject to criminal prosecution in any circumstances.
 

15. "Secondly, you have sought my opinion as to whether parents who fail to provide medical services to children on the basis of religious beliefs will be subject to prosecution for such failure.  Also, you have restated a concern of the Department of Health, Education and Welfare as to whether services will be available to children who are unable to obtain medical assistance because of their parents' religious beliefs.
"The Massachusetts child abuse reporting law does not specifically address itself to the relationship between the religious beliefs of the parent and failure to provide medical care.  However, G.L. c. 273, § 1 does address itself to that precise issue.  General Laws, c. 273, § 1 provides, inter alia, as follows:
'A child shall not be deemed to be neglected or lack proper physical care for the sole reason that he is being provided remedial treatment by spiritual means alone in accordance with the tenets and practice of a recognized church or religious denomination by a duly accredited practitioner thereof.'
"General Laws, c. 273, § 1 is a criminal statute and it expressly precludes imposition of criminal liability as a negligent parent for  failure to provide medical care because of religious beliefs.  However, the intent of Chapter 119 is, clearly, to require that children of such parents be provided services whenever the need arises.  Clearly under Chapter 119 children may receive services notwithstanding the inability to prosecute parents in such cases."

 Although the Twitchells were not aware of the Attorney General's opinion, they knew of a Christian Science publication called "Legal Rights and Obligations of Christian Scientists in Massachusetts." . . .

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 . . . . It is obvious that the Christian Science Church's publication on the legal rights and obligations of Christian Scientists in Massachusetts relied on the Attorney General's 1975 opinion.  That opinion was arguably misleading because of what it did not say concerning criminal liability for manslaughter.  If the Attorney General had issued a caveat concerning manslaughter liability, the publication (which, based on such portions of it as appear in the record, is balanced and fair) would have referred to it in all reasonable likelihood.  [p. 128] Nathan Talbot, who served as the Committee on Publication for the church and with whom the Twitchells spoke on the Sunday or Monday before Robyn's death, might well have given the Twitchells different advice.

 Although it has long been held that "ignorance of the law is no defence" (Commonwealth v. Everson, 140 Mass. 292, 295, 2 N.E. 839 [1885] ), there is substantial justification for treating as a defense the belief that conduct is not a violation of law when a defendant has reasonably relied on an official statement of the law, later determined to be wrong, contained in an official interpretation of the public official who is charged by law with the responsibility for the interpretation or enforcement of the law defining the offense.  See Model Penal Code § 2.04(3)(b) (Proposed Official Draft 1962). Cf. United States v. Pennsylvania Indus. Chem. Corp., supra 411 U.S. at 673- 674, 93 S.Ct. at 1816-1817. [n. 16]  Federal courts have characterized an affirmative defense of this nature as "entrapment by estoppel."  See United States v. Levin, 973 F.2d 463, 468 (6th Cir.1992);  United States v. Smith, 940 F.2d 710, 714-715 (1st Cir.1991);  United States v. Austin, 915 F.2d 363, 365-366 (8th Cir.1990), cert. denied, 499 U.S. 977, 111 S.Ct. 1626, 113 L.Ed.2d 722 (1991);  United States v. Tallmadge, 829 F.2d 767, 773-774 (9th Cir.1987).  "Entrapment by estoppel has been held to apply when an official assures a defendant that certain conduct is legal, and the defendant reasonably relies on that advice and continues or initiates the conduct."   United States v. Smith, supra at 714.  The defense rests on principles of fairness grounded in Federal criminal cases in the due process clause of the Fifth Amendment to the United States Constitution.  See United States v. Levin, supra at 468;  United States v. Smith, supra at 714;  United States v. Austin, supra at 366.  The defense generally involves factual determinations (see United States v. Levin, supra at 468) based on the totality of the circumstances attending the prosecution (see United States v. Smith, supra at 714), although [p. 129] the authority of the government official making the announcement is obviously a question of law.
 

16. There is special merit to such a rule if religious beliefs are involved and if the defendant was attempting to comply with the law while adhering, as far as possible, to his religious beliefs and practices.

 The Twitchells were entitled to present such an affirmative defense to the jury.  The Attorney General was acting in an area of his official responsibilities.  He is the chief law officer of the Commonwealth, with the power to set a unified and consistent legal policy for the Commonwealth.  See G.L. c. 12, § 3 (1992 ed.);  Feeney v. Commonwealth, 373 Mass. 359, 363- 364, 366 N.E.2d 1262 (1977);  Secretary of Admin. & Fin. v. Attorney Gen., 367 Mass. 154, 159-163, 326 N.E.2d 334 (1975).  See also G.L. c. 12, § 27 (1992 ed.).  He is statutorily empowered to "give his opinion upon questions of law submitted to him" by the executive branch or the Legislature.  G.L. c. 12, § 9 (1992 ed.).  Whether a person would reasonably conclude that the Attorney General had ruled that § 1 provided protection against a manslaughter charge is a question of fact.  Whether the defendants in turn reasonably relied on the church's publication and on the advice of the Committee on Publication, assuming that the construction of the Attorney General's opinion was reasonable, also presents questions of fact. See United States v. Levin, supra at 465 (notice of Federal agency approval of contemplated actions sufficient when received indirectly).  In the resolution of these factual questions, the relevant portion of the Attorney General's opinion and the relevant portion of the church's publication will be admissible.  The jury should also be advised of the terms of the spiritual treatment provision of § 1.

 . . . . For these reasons, the judgments must be reversed, the verdicts must be set aside, and the cases remanded for a new trial, if the district attorney concludes that such a prosecution is necessary in the interests of justice.

 So ordered.