41% of youths resident in Dublin's Oberstown Detention Centre experience mental health issues.
The facility presented the issue as part of its annual report for 2019, which has found a quarter of residents were on a form of psychiatric medication.
57% were not in the education system, before they went into the detention centre.
Former prison governor John Lonergan has said the facility's report shows many of the children come from 'troubled' backgrounds.
"What it indicates is that the young person has difficulties from a very early age.
"Criminality emerges as part of that whole cycle, but dropping out of education is a regular pattern.
"And when they do graduate into more serious crime later in their lives, that lack of education is a serious inhibiting factor."
Earlier this week, an analysis of youths detained at the facility in the first quarter of 2019 found one in five came from a Traveller background, echoing a trend seen in other years — 23% in 2017 and 22% in 2018.
Traveller representative body Pavee Point said the figures reflected a wider trend in the criminal justice system.
“Unfortunately, this is nothing new," said Martin Collins of Pavee Point.
"This has been a consistent concern over many years where young Travellers are disproportionately represented in Oberstown."