Under the Australian government's overseas processing arrangements, the Immigration Minister ceases to be the legal guardian of unaccompanied minors once they are sent offshore.
The Greens' call comes amid allegations of sexual assault on Manus Island and reports two unaccompanied teenage boys are being held in virtual isolation and under 24-hour surveillance after one of the boys attempted self-harm.
Leader Christine Milne says Australia must take responsibility for the boys.
"Australians need to know that Tony Abbott thinks it's okay to send children to Manus Island with no legal guardian. The government has determined that the minister doesn't have to be the legal guardian for unaccompanied children and they've virtually thrown away the key."
