Attorney-General Simon Corbell said it was reasonable and responsible for the Chief Minister and government ministers to report cases where the law may have been broken.

"The Chief Minister has acted entirely appropriately," he said.

"If a person contacts the Chief Minister or me as the Attorney-General and indicates that they may be involved in a breach of the criminal law, it's entirely appropriate and I think incumbent on a public office holder to refer that information to the relevant agencies."

ACT's recently retired public advocate, Anita Phillips, a director of the board of the Australian Association of Social Workers, has backed Ms Gallagher's decision to make the report.

"I support the Chief Minister in making this report because she, as a person in a position of authority, had information that she suspected that this child could be at risk because the child was being administered an illegal drug," she said.

"All of the things that flow on from that are collateral damage, unfortunately, but she had no option but to do that report."

Mandatory reporting laws require certain professions, including teachers, doctors and police, to report cases of sexual abuse and "non-accidental injury" of children but child protection laws also allow for the voluntary reporting of child abuse and neglect. Government ministers are not considered "mandated reporters" under the laws.

ACT Children and Young People Commissioner Alasdair Roy said there should be voluntary reporting of cases where a person believes a child might be at risk of abuse, harm or neglect.

"If anyone, and that includes the Chief Minister, is concerned about the safety or wellbeing of a child, then they should do something about it. So, if the Chief Minister felt she needed to tell someone, then I can't criticise or comment on that," he said.

Mr Corbell said it was not up to Ms Gallagher to decide whether the law had been broken.

"Members of the public would expect ministers to act in accordance with the law and where a possible breach of the law is brought to their attention, it is reasonable and the responsible thing to do to refer it to the relevant agencies for advice and for those agencies to then decide whether or not further action should be taken," he said.

A Community Services Directorate spokesman said reporting of child protection concerns was a "critical mechanism" to ensure the safety and care of children and young people.

He said providing an illegal substance to a child or young person would require "consideration" by Care and Protection Services and might result in a child protection investigation.

"It is the responsibility of Care and Protection Services to provide information to the Australian Federal Police where a child concern report includes information that may be a criminal offence," he said.

Mr Corbell said possessing marijuana was still illegal in the ACT and supplying it was a serious criminal offence.

"Whilst there is a live, legitimate policy debate about whether or not the law should be changed [to legalise medical marijuana], right now the law does make marijuana illegal and it is entirely responsible that an elected office holder referred any possible breaches of the law to relevant agencies," he said.

Ms Phillips believed Ms Gallagher had no choice but to report the case to authorities.

"The complexity of the values and the best interests and the ethical considerations in this particular case are just an example of how difficult that interface between the law and ethics and morals can be, but the law is the law and must be abided by," she said.