Eleven children were moved off Nauru for medical treatment on Monday, Australian Border Force has confirmed.
The cohort was transferred hours before ABF bosses fronted a Senate estimates hearing on Monday night and coincided with a significant increase in medical transfers off the Pacific Island in the past few months.
Border Force originally said 16 were transferred but later clarified that 11 were moved on Monday to Australia for medical treatment.
They join more than 600 people in Australia on "temporary transfers" from offshore detention.
Border Force said 652 people, including 52 children and 107 families, remain on Nauru while 626 men are on Manus Island in Papua New Guinea.
The vast majority on both islands have been judged to be genuine refugees.
Border Force's surgeon-general and de-facto chief medical officer for offshore asylum seekers, Parbodh Gogna, said medical staff on Nauru had "seen an unprecedented jump" in people presenting for medical care in the last couple of months.
Patients were treated for mental and physical illnesses but the reason for the uptick was unclear, he said.
But Dr Gogna said he heard anecdotes that years of detention, a break down of resilience and unwellness of parents transferring to children were factors.
He said Nauru has multiple medical facilities but lacked highly specialised health care for children.
The Home Affairs department said it had spent $480,000 in legal fees in just three months responding to applications to have refugees medically transferred to Australia from Manus Island and Nauru.
The figure from July to September far outstrips spending for the entire previous financial year, with $275,000 spent on such legal fees in 2017-18.
The committee was told, for example, there were just five applications lodged between May and June this year.
Home Affairs Secretary Michael Pezzullo said permanent asylum in Australia wouldn't be granted to those transferred for medical treatment because it could incentivise "perverse behaviours", including causing serious harm to instigate a transfer.
"Treatment in Australia is absolutely available for those who require it," he told Senate estimates on Monday.
Prime Minister Scott Morrison is under immense pressure to get sick refugee children and their families off Nauru.
He has said he is willing to accept New Zealand's offer to resettle asylum seekers and their families from the Pacific island, on the condition they never come to Australia.
Labor frontbencher Tony Burke said his party was sceptical about the bill, which has been stuck in parliament for almost two years.
"There are deep, deep problems with that bill," he said.
Three Liberal MPs - Russell Broadbent, Craig Laundy and Julia Banks - last week demanded Mr Morrison get children off Nauru.
Australian Associated Press