84 children were admitted to adult psychiatric units last year, figures released to Fianna Fáil show.
This was an increase from 82 in 2017 and 68 in 2016.
The information was provided by the HSE to Fianna Fáil's spokesperson on mental health James Browne, who said the figures were "a shocking indictment" of the government's action on the issue.
"After a number of years of progress, things are now actually going backwards," Deputy Browne said.
“The Mental Health Commission has previously said that such admissions are a clear breach of the human rights and dignity of a child.
Ten beds at St Ita’s in Portrane are set to open in 2020, as well as an additional 20 beds in the National Children’s Hospital in 2022.
However, Deputy Browne argued that the beds may not be suitable for every child and risk being oversubscribed.
He said there are "serious problems" in maintaining the current beds in use because of staff shortages.
“This government is continuing to fail young people needing access to mental health services," he said.
"The total number of Child and Adolescent Mental Health Services staff is still barely over half what was recommended in the flagship 2006 policy. This issue needs to be tackled urgently."
In its reply to Deputy Browne, the HSE said: "The HSE is committed to age appropriate placement and to the minimisation of the number of admissions of children to adult units, while acknowledging that, in exceptional circumstances, it will continue to be necessary, where there is a clear clinical imperative, to admit a small number of children to adult units, for the shortest time possible.
"Children are admitted to adult units after efforts to place them in a Child and Adolescent In Patient Units are unsuccessful due to capacity or clinical needs.
"The National CAMHS Lead works closely with local and national CAMHS in-patient services to ensure that the clinical needs of the young person are assessed and addressed within the most appropriate setting for that young person and their family."