Ten members of staff at a children's detention centre have been on sick leave for more than a year, it has emerged.
Children's Minister Frances Fitzgerald said a third of beds at the facility in Lusk, Co Dublin, are lying empty because of staffing problems and issues with a roster implemented in February.
A Government decision to stop sending 16-year-olds to adult prisons coincided with a spike in judges remanding teenagers, putting demand at Oberstown campus at a record high, she added.
But her officials said it was wrong to link sick leave levels with the older teenagers being moved to the units.
Jim Breslin, secretary general of the Department of Children and Youth Affairs, said: "It is a problem on campus, not specifically related to the arrival of 16-year-olds. It's pointing the finger in the wrong direction."
The pair appeared before the Oireachtas committee on health and children, where ombudsman for children Emily Logan on Wednesday queried concerns from staff on the campus of the Oberstown detention schools that they are not trained to deal with older boys.
Mr Breslin and the minister denied the claims, adding that its 190 care staff were qualified and skilled.
Oberstown began receiving 16-year-old boys last year from St Patrick's Institution, which was heavily criticised in prison reports. However judges recently complained about the lack of room for young offenders, who they have been forced to free back on to the streets with serious convictions.
Sinn Fein's Caoimhghon O Caolain said "critical steps" are required to tackle the problems on site. He added: "It is clear from voices inside and outside the campus that there is an absolute requirement for additional staff to ensure the facility can be fully utilised and is fit for purpose for detainees and for those who work across that campus."
There are 24 beds in Trinity House School - including eight waiting to open - 20 in Oberstown Boys School and eight in Oberstown Girls School which are rarely full. Ms Fitzgerald said talks were still continuing with unions to open a new eight bed unit on the grounds, adding that temporary or agency staff would have to be taken on.