Senators Ricky Muir and Nick Xenophon are seeking urgent answers on why children who were removed from Christmas Island are still being held in a detention facility in Darwin, despite former immigration minister Scott Morrison's promise that they would be living in the community.

The former immigration minister had promised in December all children would be removed from Christmas Island by Christmas and placed into the community, in return for the crossbenchers' support of Mr Morrison's wide-ranging and controversial changes to the Migration Act.

Asylum seekers who were in detention at Christmas Island. Credit:Wolter Peeters

Senator Muir, who was the final senator to agree to the changes of the Act, said he had immediately rung the minister's office after discovering that the children were still being detained at Blaydin Alternative Place of Detention, as revealed by Fairfax Media on Thursday.

"Early 2015 is not good enough and I am currently seeking an urgent update on when the children and families will be released in to the community," Senator Muir said.