Law reform advocates say it's a tentative step towards keeping children out of prisons.

A Greens motion calling on the government to support the change passed the ACT Legislative Assembly on Thursday.

The government agreed to start early planning so the next government could legislate raising the age of criminal responsibility.

Attorney-General Gordon Ramsay said he still supported a national approach through the Council of Attorneys General.

Attorneys-general have delayed a decision about whether to support raising the age until 2021.

"It's very clear that the best outcome for the children of Australia ... would be for us to have national consensus on this matter," Mr Ramsay said.

"I will continue work with other jurisdictions and we want to make sure that children are diverted from the criminal justice system.

"It's certainly not a stroke-of-the-pen sort of thing.

"It's been talked about a couple of times in some of the advocacy that it's a very simple legislative amendment.

"It might be the stroke of a pen in terms of turning 10 to 14 in legislation, but this is a complex area and for the sake of the children ... we have to make sure it's done well, it's done correctly, and not done in a half-thought-out way."

The government has said there should be exemptions for more serious offences.

Greens leader Shane Rattenbury called on other states and territories to follow the ACT's lead.

"Children as young as 10 simply don't belong in prison," he said.

"Where children are imprisoned, it sets the trajectory for the rest of their lives and increases the risk they will be involved in the adult criminal justice system as they mature.

"We can better support these children by providing them with the help they need to stay on the right path.

"Australia's minimum age of criminal responsibility of 10 is well and truly out of step with the rest of the world, and we have been chastised for this by the United Nations Committee on the Rights of the Child.

"With the right supports in place, and a well-resourced youth sector, we can provide better alternatives to custody for children under 14."

ACT Law Society president Chris Donohue said it was a first tentative step towards changing the law.

"We are cautiously optimistic about today's decision," he said.

"The proposal, brought before the Assembly by Shane Rattenbury MLA, brings us one step closer to this much-overdue reform.

"We should be treating children like children, not criminals."

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Mr Donohue said the changes needed to happen sooner rather than later.

"The Law Society welcomes Attorney-General Ramsay's public support of this reform and for identifying a clear way forward," he said.

"We are pleased to see the ACT taking a leadership role in this very necessary change.

"However, there is a need for action on this reform to be taken more quickly.

"The Law Society, and our specialist legal committees, stand ready to assist the ACT government with the next steps."

In July, leaders in the ACT's youth, health, legal and community sectors jointly penned a letter urging the territory government to lift the age of criminal responsibility.