The committee estimated that 126 children are currently held in detention in Australia, and another 116 are in a facility on the small Pacific island of Nauru.

Pezzullo claimed, however, that in the "difficult" cases of at least 19 children in detention whose relatives are suspected of criminal offenses, release may take "months or longer."

A study by the Australian Human Rights Commission revealed that more than 300 children in Australian immigrant detention centers committed self-harm or threatened to commit self-harm between January 2013 and March 2014 trying to protest against intolerable conditions and human rights violations.

The number of children detained on Nauru will soon increase by almost 50 percent, when those who underwent medical treatment in Australia will be sent back to the island again, the secretary added.

Earlier this month, the Australian Human Rights Commission said in a report that the country's unjustifiably prolonged immigration detention of children has profoundly negative effects on their mental and emotional development, and violates international human rights law.

The report found that during the 15-month period studied, more than 300 children committed or threatened self-harm, almost 30 went on hunger strike and other 30 reported sexual assaults.