The number of children behind bars in NSW prisons has fallen to a "new historic low" after two years of the COVID-19 pandemic.
A Bureau of Crime Statistics and Research report on custody data shows 161 people under the age of 18 were in prison in December, a fall from 184 a year earlier and down 40 per cent since 2019.
BOCSAR executive director Jackie Fitzgerald said the juvenile prison population was at its lowest since the bureau started collecting data in 2010 and was likely lower than it had been in at least 20 years.
The NSW adult prison population was 12,168 in December, including 7722 sentenced and 4446 on remand, down more than 10 per cent on pre-pandemic levels and at its lowest since 2015.
Ms Fitzgerald said most crime had fallen dramatically during the pandemic, reversing a rising trend in offending and incarceration.
"The lockdowns really reduced crime considerably, but they also posed risk for prisons," she said.
"We've seen some changes in decisions made by bail authorities ... but we're also seeing changes in the volumes of offenders. We've seen the suspension of court matters as well."
Ms Fitzgerald said BOCSAR had expected prison numbers to "rebound" after the first pandemic lockdown in 2020, "but that's not really what we saw".
"Almost every offence has fallen. The offence that hasn't fallen is domestic violence, in terms of police records.
"During those lockdowns we saw huge falls in theft offences, violence.
"Some of those bounced straight back once the lockdown was lifted.
"That happened with violence offences, but property crime still hasn't come back.
"We've got much lower levels of break-ins than we did pre-pandemic.
"The impact has endured longer than we would have thought."
The number of adults in prison for unlawful entry and burglary fell 117 year-on-year to December.
The number of people locked up for robbery (-94), fraud (-83), acts intended to cause injury (-88) and justice procedure offences (-70) also dropped.
But the number of prisoners behind bars for sexual assault offences rose by 67. Sex offenders make up one fifth of the prison population who have been sentenced.
Sex offence charges increased 18.5 per cent from 2000 in 2016-17 to 2370 in 2020-21 and the conviction rate remained stable at just over 60 per cent.
Less than 4 per cent of the NSW population is Aboriginal, but indigenous people made up 42.9 per cent of the juvenile prison population in December and 27.5 per cent of adults in prison.
