A 13-year-old Indigenous Australian boy spent 45 days in solitary confinement while being held for minor offences, in the latest youth justice case to raise human rights concerns in Queensland.
The boy - referred to as "Jack" - was released on probation last week after 60 days in custody at Cleveland Youth Detention Centre in Townsville.
He is understood to have spent 22 consecutive days in isolation.
Queensland's human rights chief says the case may have broken state laws.
"If he's being locked in because there's staff shortages, and Cleveland detention centre has 80 or more kids in at any one time, one can only assume that other kids are in the same circumstance.
"You would hope not, but maybe it's more common than we thought."
Jack's period of detention included six days being held in adult prisons. He was released last week with a verbal reprimand.
A separate recent case also raised human rights concerns over the Queensland's youth justice system, which is currently undergoing reform.
In February, it emerged that another 13-year-old Queensland boy with developmental disabilities spent 78 days confined to a cell for 20 hours per day.
Queensland is currently debating new laws which would criminalise bail breaches by minors - a change which will cause the youth prison population to increase dramatically, experts warn.
State Human Rights Commissioner Scott McDougall said the recent cases may have breached Queensland's Human Rights Act, which states all prisoners should have access to fresh air and exercise for a minimum of two hours a day.
He warned that changes to the law would only make the situation worse, and that immediate steps were needed to stop children being placed in isolation.
"Unfortunately, I don't think they're isolated cases," he told the BBC.
"Given the laws that are [being] passed in Queensland, which are clearly intended to incarcerate more children, it becomes even more important that the government urgently develops a coherent plan for preventing children coming within the criminal justice system, " he said.
"My concern is by increasing the pressure on the system, we risk normalising the mistreatment of children".
Mr McDougall urged the state government to "double down" on measures to keep children in school and stop them going down "the path of criminalisation".