A record number of children are being held in closed immigration detention - despite the government's pledge most would be out by last June.

Almost 2000 asylum-seeker children are being held on Manus Island, Christmas Island and elsewhere in forms of detention that restrict their movements.

Advocacy groups and politicians say the children are being held in contravention of their human rights, and often in harsh, remote environments.

Despite the federal government policy that ''children not be held in immigration detention centres'', the numbers now are even greater than when former immigration minister Chris Bowen said the aim was for the ''majority'' of children to be out of detention by June 2011.

Refugee Council of Australia president Phil Glendenning said the numbers were a record and represented ''a fundamental failure of policy''.