The Ombudsman for Children has told an Oireachtas Committee that the practice of admitting children to adult psychiatric facilities must end.
Niall Muldoon said a habit had built up that it was okay when there were not enough beds, but he said that was not okay anymore.
He told the Oireachtas Sub-Committee on Mental Health that his office had spoken to children who had been in such facilities about the trauma they went through.
"While they were at their lowest ebb in life, they may have been suicidal, they may have already attempted something, the best service we could offer them was an adult psychiatric ward which is scary at the best of times. We cannot allow that to happen anymore."
The committee is examining the Mental Health (Amendment) Bill.
Mr Muldoon said he welcomed that the Bill makes it standard that children should be cared for and treated in an age-appropriate environment.
However, he objected to the reference to doing this "in so far as practicable" and he said that meant it allowed the admission of children to adult inpatient facilities.
He said that was a symptom of a systemic failure on the part of the State which had been maintained over many years.
"If we continue the way it is, we will be legislating this into practice - we will need [an] amendment to stop it. It must be a zero option."
Sinn Féin's Mark Ward said the practice was draconian and must be stamped out.
He said that 27 children were admitted to adult facilities last year although he acknowledged that this figure was lower than in previous years.
Karen McAuley, head of policy with the Ombudsman for Children, said the bill would establish a legal basis for admitting children to adult facilities.
"If we do this, it may exacerbate what we already know is a protracted delay in implementing measures and putting in resources and ending this practice."
Green Party TD Neasa Hourigan said she absolutely supported the idea of zero tolerance for admission of children to adult facilities.