Australian of the Year Patrick McGorry, who has called detention centres factories for mental illness, joined the Greens' immigration spokeswoman Senator Sarah Hanson-Young in Melbourne on Monday to announce the party's plan to get children out of immigration detention.
When the Senate resumes sitting in two weeks, the Greens will move an amendment to the Migration Act to exempt children from the mandatory detention clause.
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But neither Labor or the coalition are likely to support the move.
"It's time that we gave some legal safeguards to keep children out of immigration detention," Senator Hanson-Young told reporters.
"There are 700 kids in immigration detention today, we need to see them released, they need to be living in the community while they wait for their claims to be processed."
The Greens also want the Community Assistance Support program expanded and a Commonwealth Commissioner for Children and Young People established.
Professor McGorry said he was not aligning himself with the Greens by helping the party to launch its policy and he had no plans to enter politics.
"I'm not aligning myself with any political party, I'm just stating the facts about the effects of mandatory detention," he told reporters.
"Prolonged detention of anyone beyond a short period is harmful to mental health.
"Everyone accepts that, so I think it's vital to move on implementing policies which prevent this from happening."
Senator Hanson-Young could not provide figures on how much the Greens' proposals would cost.
She called on the government to submit the Greens' plans to treasury for costing.
Professor McGorry said detainees often suffered anxiety, depression, trauma symptoms and behavioural withdrawal.
"It's very hard for the children and young people to have normal developmental experiences when they are held in detention," he said.
"They can't attend normal schools typically, although on Christmas Island the young people do attend the local school."
Professor McGorry said most Australians wanted children out of detention.
"I don't believe ordinary Australians want this to happen," he said.
"Ordinary Australians are decent people, if they are aware of what is happening to these children and young people in these settings ... the vast majority of Australians would not support this."
The Hotham Mission Asylum-Seeker Project works with asylum seekers who are facing homelessness as they wait for the refugee claims to be processed.
Director Caz Coleman said asylum seekers have better settlement outcomes when they are able to exercise more choice over their lives.
"Community care also facilitates a higher rate of successful voluntary return than it does from a detention environment," she told reporters.
