On Sunday, Immigration Minister Peter Dutton said he felt "a great sense of achievement" at having moved into the community the final 43 children who were held in onshore detention at the end of February. About 50 children also remain in detention on Nauru.

He rejected a report published by Guardian Australia suggesting the government had simply reclassified sections of detention centres as "community detention" in order to make the claim.

"The same definitions apply today as they did before," Mr Dutton said. "There are certain characteristics that need to be met in relation to all these definitions, but that's all beltway stuff."

Pushed on the question of whether the children were really out of detention, he told reporters: "They're outside of 'held detention', so that's the answer that I've provided to you before."

Fairfax Media understands that in at least one case, a family remains in immigration-controlled residential housing near the Villawood detention centre in Sydney, but they have been granted free movement. It is understood the children's father remains detained at Villawood due to an adverse security finding by ASIO.

In respect of those circumstances, a spokeswoman for the minister told Fairfax Media: "There are arrangements that have been put in place. Those arrangements now sit with the fact that it's community detention."

Mr Dutton's office did not respond to requests for further clarification on Sunday. On Monday morning the minister told ABC radio the special arrangements described above only involved one family, located at Villawood.

Before the 2013 election, the number of incarcerated children peaked at close to 2000, in what the government argues is the shameful legacy of Labor's failed border protection policies.

Those families who have been released from "held detention" are now in community detention, which means they reside in community housing at a specified address, but are generally free from physical supervision. Legally, they remain in immigration detention and the responsibility of the minister.

Australian Human Rights Commission president Gillian Triggs said she "warmly" welcomed the announcement, while Prime Minister Malcolm Turnbull said it was the realisation of a long-held government priority.

"The real message here is that we have stopped the boats," he said.

But the threat of return to Nauru still hangs over about 150 people, including children and their families, who were transferred to Australia for medical treatment. And 50 minors remain in Australia's offshore detention facility on Nauru, in conditions the United Nations has described as "harsh" and short of international standards. There are no children in detention on Manus Island, according to the most recent department statistics.

Refugee Action Coalition spokesman Ian Rintoul welcomed the development but described it as a "really qualified shift" from the government.

"There's a bit of administrative sleight of hand," he said. "The position of people who remain in community detention is no clearer."

Mr Rintoul said he still had "enormous concerns" about the future of families in community detention, particularly those who could be returned to Nauru.

Greens Senator Sarah Hanson-Young called on Mr Turnbull to rule out returning any children to Nauru and to close the detention centre on the island nation.

"Clearly, Malcolm Turnbull is seeing that the Australian public don't want to see children being used in this political point-scoring game on who can be toughest on refugees," she said. "In order to pay proper credit to that, he must close Nauru and bring all of those families and those hundreds of children here to Australia."

- with Jane Lee