Queensland’s public guardian has expressed grave concerns about children being “held like caged animals” in police watch houses intended for adult offenders, often for weeks at a time.

The ABC’s Four Corners program has obtained hundreds of documents that detail cases of children enduring lengthy periods in adult holding cells because the state’s youth detention centres are full.

“We have significant numbers of kids, from traumatised backgrounds, held like caged animals in concrete pens,” Public Guardian Natalie Siegel-Brown told the ABC.

She cited one particularly alarming case where a girl was accidentally put in with two alleged male sex offenders.

Four Corners has obtained 516 files, including reports to Ms Siegel-Brown’s office, about the treatment of children in Queensland’s criminal justice system.

They detail how kids as young as 10 have been held in watch houses, sometimes in isolation, sometimes in so-called suicide smocks.

More than 70 files related to children who spent 10 or more days in adult watch houses. Two children were held for 33 days or more.

One was an Aboriginal boy who had been deemed permanently unfit to plead and assessed as having the cognitive function of a child aged younger than six.

In another case, a girl was put into a pod with two alleged male sex offenders at the Brisbane City Watch House.

At the same watch house, a different girl was held 25 days, during which time she discovered she was about 11 weeks pregnant. She was later transferred to a youth detention centre.

Queensland’s youth detention centres are full after state government reforms mandating that 17-year-olds be dealt with in the youth justice system, not the adult system.

This has resulted in children being held for long periods in adult watch houses because there’s nowhere else for them to go.

Last month, the Labor government said it would spend $150 million on a new 32-bed youth detention centre at Wacol, and $27 million on 16 more beds at the existing Brisbane Youth Detention Centre. It’s also funding diversion programs aimed at preventing youth crime.

Child Safety Minister Di Farmer said there was no doubt that adult watch houses were poor environments for young people. But she would not say when kids would stop spending long stings in adult holding centres.

“I don’t like to give a definite date. I would hope by the second half of next year we can see that there are only kids in watch houses who are really just there as the general process of things,” she told Four Corners.

The opposition said the Premier had failed to plan for the consequences of her own reforms.

“This scandal is a direct consequence of Annastacia Palaszczuk’s failure to plan for enough youth detention beds while simultaneously adopting a policy to move 17-year-olds out of adult prisons,” Liberal National Party leader Deb Frecklington said.

-AAP