Twenty-three Indonesian youths plan to sue Australia for illegal detention after being jailed in adult prisons for people-smuggling when they were minors, a child rights agency said on Tuesday.

Australian authorities detained the boys as adults between 2008 and 2011, following wrist X-ray tests to determine they were over 18 years old – a method which has been criticized by some experts as outdated and unreliable.

"The plaintiffs are looking for compensation and an apology from Australia so they can receive an education and live normal lives," Indonesia's National Commission for Child Protection deputy chief Apong Herlina told AFP.

The commission is working on the case with an Indonesian and an Australian lawyer to file the civil suit in an Australian court.

Indonesian lawyer Lisa Hiariej told AFP that she was also investigating claims by two of the plaintiffs that they had been sexually harassed by adult male prisoners in Sydney's Silverwater jail.

"The prisoners never touched the boys with their hands but showed them [their genitals]," Hiariej said. "They were shown how to do sex with body language."

Australia's human rights commission reported last year that 180 Indonesians in Australia suspected of people-smuggling claimed to be minors, some of whom were obviously children and were immediately repatriated.

But 48 boys – aged 14 to 17 – were jailed with adults based on the wrist test and had therefore been illegally detained, the report said.

Herlina said many of the boys appeared to be older according to the X-ray test because daily laborious work as fishermen had made their wrists "more developed".

A spokesperson from the Australian Attorney-General's Department said the government had not received any formal notification of the claim.

Indonesia has long been a transit country for illegal migration to Australia. Crew that take rickety boats out on the perilous journey often come from poor fishing communities.