In a harrowing report released on Tuesday, WA's custodial services inspector says there were 24 suicide attempts at Perth's Banksia Hill detention centre between January and November last year.
Most involved several boys who had formed a suicide pact while being held under observation in the facility's "intensive support unit" (ISU).
One 16-year-old boy made five attempts on his life in one month and had to be resuscitated in his cell.
Inspector Eamon Ryan also found there had been several days in November when four ISU detainees spent less than an hour outside their cells.
"We concluded that their human rights were being breached on those occasions," he said.
The United Nations' Mandela rules, which are not legally enforced in WA, require that detainees spend at least two hours out of their cell in a 24-hour period.
Mr Ryan delivered the findings after visiting Perth's Banksia Hill last December, describing conditions there as severely understaffed and "inhumane".
The unscheduled visit, which followed an increase in self-harm and staff assaults, resulted in WA's Department of Justice being issued with a rare show-cause notice.
Australian Lawyers Alliance spokesman Greg Barns SC said the treatment of detainees amounted to abuse and would expose the WA government to compensation claims.
Save the Children Australia labelled the findings appalling and called for the eradication of solitary confinement at youth detention centres.
Amnesty International said the report was shocking but not surprising, having called for the ISU to be closed in 2018 amid abuse allegations.
"These kids need our help to get back on track, not to be sent to places that harden their trauma into life-long calluses," Amnesty's Indigenous rights advisor Rodney Dillon said.
Mr Ryan warned that detainees with pre-existing trauma and cognitive impairments were being denied meaningful interaction, resulting in more instances of self-harm.
Hundreds of former detainees have signed up for a class action alleging mistreatment at the facility.
The McGowan government will invest $25 million into Banksia Hill in next month's budget, which will largely fund infrastructure upgrades.
WA's justice department is developing "a new operating philosophy and service model" that will be guided by trauma-informed principles.
It said conditions at Banksia Hill had improved since the inspection and about 40 staff had recently started working there.
Commissioner for Children and Young People Jacqueline McGowan-Jones said many Banksia Hill detainees were on remand.
Some had been granted bail but had nowhere safe to go.
"There's no doubt that these young people have done some very bad things, some of them. But they are not bad people," she told ABC radio.
"They are children. They have really suffered great disadvantage and the system, rather than supporting them for rehabilitation ... is instead caging them."
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