Concern has been raised about children being “held like caged animals” in police watch houses intended for adult offenders.

The ABC has revealed details of cases of children enduring lengthy periods in adult holding cells in Queensland 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.

In one case, she said a girl was accidentally put in with two alleged male sex offenders.

Reporters obtained over 500 files, including reports to Ms Siegel-Brown's office, about the treatment of children in Queensland's criminal justice system.

They describe kids as young as 10 being held in watch houses, sometimes in isolation, sometimes in so-called ‘suicide smocks’.

Many children spent 10 or more days in adult watch houses, while two children were held for 33 days or more.

Queensland Child Safety Minister Di Farmer has pledged to correct the situation, but could not provide a timeline.

“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 full report is accessible here.