Immigration Minister Peter Dutton has confirmed dozens of children will be returned to Nauru, one day after announcing there were no children in mainland detention.

The Federal Government yesterday announced no asylum seeker children remained in Australian detention centres, with the final children being released from Darwin on Friday evening.

About 50 asylum seeker children remain on Nauru.

The ABC understands on the same day the last children in Australia were freed, an Immigration Department facility directly outside Villawood Detention Centre had locks removed and security altered.

Its residents have now been given the same freedoms as those in community detention.

But approximately 90 children currently in Australia are due to be sent to Nauru, following a High Court decision earlier this year.

Mr Dutton told the ABC the Government's policy had not changed in relation to the children, who are currently in Australia either for medical treatment or accompanying a family member to hospital.

"[They are] all subject to go back to Nauru once medical support has been provided and we've been very clear about that," he said.

"We're happy to make third-party arrangements, we offer settlement packages and talk individually with the families."

Mr Dutton said resettlement in Cambodia would be offered, urging people to deal with facts, "not the emotion".

Greens immigration spokeswoman Senator Sarah Hanson-Young called on Mr Dutton to rule out sending children in Australia back to Nauru.

"While it's good to see the Government being forced into releasing children from detention, it means nothing while the Minister plans to send them back to Nauru," she said.

"Peter Dutton should allow these families and children to apply for visas in Australia, so that they can get on with rebuilding their lives in safety."