Australia is investigating 44 allegations of sexual abuse of asylum seekers in detention centres.
Immigration official Ken Douglas told a senate committee that some of these cases involve children but could not say how many.
Local media say that the claims cover a period from January 2013 to July 2014.
Immigration Department Secretary Michael Pezzullo said on Tuesday that 126 children were still in immigration detention.
Speaking at a senate committee hearing in Canberra, he said that less than 20 of these children were facing long-term detention.
"There are 19 children in families where there are law enforcement or national security issues pertaining to an adult relative," he said according to the News Corp website.
Mr Pezzullo added that he had ordered an examination of all of the incidents involving the alleged abuse of children dating back to 2008.
Sexual assault Earlier, local media reported that the immigration department said that some of the 44 allegations of sexual abuse at detention centres involved children.
Mr Douglas was quoted by ABC News as saying that they "represent sexual assaults involving a minor, to a minor or in a detention facility in which a minor was accommodated."
He added that, at this time, it was not possible to determine whether all of the reports related to minors or not.
The senate committee also heard that there had been 19 reported cases of sexual assault at the Nauru Island detention facility over the past two years, according to the Sydney Morning Herald newspaper. Five of them involved children.
The News Corp website reported that Assistant Immigration Minister Michaelia Cash had told the committee that the government was doing everything possible to remove children from detention facilities.
Successive Australian governments have been heavily criticised over their harsh asylum policies, under which asylum seekers are detained for long periods in offshore camps while their applications are processed.
Australia currently detains all asylum seekers who arrive by boat, holding them in offshore processing camps. Those found to be refugees will not be permanently resettled in Australia.
Forgotten children The allegations of sexual assault come less than two weeks after a report by the Australian Human Rights Commission (HRC) which condemned the current treatment of children of asylum seekers.
The report, entitled The Forgotten Children, said a third of detained children have developed mental illnesses of such severity that they required psychiatric treatment.
The HRC said that detaining children violates international human rights law and called for their immediate release.
The Commission's President Gillian Triggs wrote: "The aims of stopping people smugglers and deaths at sea do not justify the cruel and illegal means adopted."
Attorney General George Brandis responded to the report by saying that the government does not accept the commission's conclusions.
Australia and asylum Asylum seekers - mainly from Afghanistan, Sri Lanka, Iraq and Iran - travel to Australia's Christmas Island by boat from Indonesia
The number of boats rose sharply in 2012 and early 2013. Scores of people have died making the journey
To stop the influx, the government has adopted hard-line measures intended as a deterrent
Everyone who arrives is detained. Under a new policy, they are processed in Nauru and Papua New Guinea. Those found to be refugees will be resettled in PNG, Nauru or Cambodia
Tony Abbot's government has also adopted a policy of tow-backs, or turning boats around
Rights groups and the UN have voiced serious concerns about the policies and conditions in the detention camps. They accuse Australia of shirking international obligations.
http://www.bbc.com/news/world-australia-31596727#