Victorian prison guards placed a spit hood on a child, effectively kept him in isolation for months and deprived him of water.
In its 2022/23 annual report, the Commission for Children and Young People revealed it was contacted in February by the teen, aged under 18 but in adult custody, after prison officers applied a spit hood to him earlier that day.
The day before the hood was applied, the youth was involved in a series of incidents and forcibly moved by staff to another cell.
The prisoner reported that after being moved, the water in his cell was turned off for about 22 hours, despite repeated requests for staff to return it.
It meant he was unable to wash his hands and use the toilet.
"I was appalled and, to be honest, I almost didn't believe it because I thought we were better than that in Victoria," Commissioner for Children and Young People Liana Buchanan told AAP.
An inquiry found the spit hood was applied despite the youth not being involved in spitting incidents and that he was kept in effective isolation for 24 weeks during eight months.
"He had little contact with other prisoners, was confined to his cell for 22 or 23 hours per day, and had no access to education and limited access to programs," the report said.
At the time, corrections regulations allowed a spit hood to be applied to a prisoner aged less than 18 as long as their age and vulnerability were considered, the report said.
Corrections Victoria has since advised the commission its policy would be updated to ban the application of spit hoods on children in adult custody.
Ms Buchanan said she was confident there were no other children in adult custody who have been subjected to spit hoods.
"But there are hundreds of 18, 19 and 20-year-olds in adult prisons," she said.
"I have no idea how commonly this might be used against other young people who might not be under 18 but are still very much developing maturity.
"The fact that this is not known to me, how prevalent this is, is of concern."
A 2017 royal commission into the Northern Territory's Don Dale Youth Detention Centre described the use of spit hoods as inhuman and recommended they be banned.
"It's almost become symbolic of abuse against children in custodial settings," Ms Buchanan said.
More broadly, the report revealed notifications of alleged child abuse and misconduct by Victorian workers and volunteers have spiked by almost 20 per cent in the past year.
The commission received 1457 notifications of alleged child abuse and child-related misconduct by workers and volunteers - an 18 per cent rise from 2021/22.
Since its reporting scheme began in 2017, notifications have grown by 81 per cent.
Each notification can include multiple allegations of reportable conduct.
The education sector led reportable notifications (30 per cent), followed by out-of-home care (28 per cent), early childhood education (26 per cent), and religious bodies (five per cent).
Physical violence was the most common allegation across all sectors (36 per cent), then behaviour causing significant emotional or physical harm to a child (22 per cent), significant neglect of a child (18 per cent) and sexual misconduct (18 per cent).
Indigenous children and young people accounted for 10 per cent of alleged victims despite only making up two per cent of Victoria's non-adult population.
In 2022/23, the commission completed 45 inquiries into deaths of children and young people who died within 12 months of their last involvement with child protection, including eight related to Aboriginal children.
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