More than 230 children were in custody in NSW in June, an increase of 34 per cent since the same month in 2023, the state's crime statistics bureau said.
It's a reversal in a trend of declining numbers of children in detention, but the figure is still lower than it used to be, the bureau's executive director Jackie Fitzgerald told AAP.
"Over the longer term, we have had much higher rates of kids in custody than we have now," she said.
More than 300 children were in custody in June 2015.
The majority of children currently in NSW jails have not been convicted, with only 66 children in custody as a result of a sentencing.Â
More than 70 per cent of the children in jail are on remand while they go through the court process.
But the increase is not necessarily driven by laws placing additional tests on bail, suggesting magistrates are increasingly inclined to refuse bail.
"There has been a tightening up of access to bail," Ms Fitzgerald said.
"But it seems to be beyond just the offences that were targeted or the particular circumstances that were targeted under the legislative change."
The state government introduced laws limiting access to bail for children aged 14 and over accused of break-and-enter and motor vehicle theft offences while bailed on similar charges.
The government has also clamped down on bail for accused domestic violence offenders.
"We have had a lot of conversation about bail and remand in NSW, both in the adult space and the youth space," Ms Fitzgerald said.
"Whether it's that, or it's something that magistrates are seeing in the court, there has been a move towards more serious bail determinations for young people irrespective of those legislative changes."
The increase is particularly concerning for Indigenous children and conflicts with Closing the Gap targets, Ms Fitzgerald added.
About eight per cent of children in NSW are Indigenous, but that proportion rises to almost 60 per cent for those in jail.
Greens MP Sue Higginson said the money spent locking up children would be better spent on social services and programs that could divert them from the criminal justice system.
"Locking up kids is the most criminogenic thing we can do to them," she said.
"It increases the likelihood of reoffending, entrenches disadvantage and drives higher crime rates."
NSW has the most people in custody in Australia but is also its most populous state.
The Northern Territory has the highest proportion of its population in jail while Victoria has the lowest, according to Australian Bureau of Statistics data.
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