A severe shortage in psychiatric services for young people resulted in 24 children under the age of 16 being admitted or detained in adult psychiatric hospitals last year.
One 15-year-old child with behavioural problems has spent more than two years in an adult psychiatric unit in Limerick.
Official figures obtained by The Irish Times show that more than 600 teenagers aged between 16 and 19 years of age were also treated in adult psychiatric hospitals last year.
Many of the children have severe behavioural difficulties and do not necessarily have a mental illness.
The head of the Mental Health Commission, the watchdog for the mental health sector, Dr John Owens, said yesterday the practice of admitting children to adult units was "unacceptable".
"Anyone under the age of 16 should never be admitted to an adult unit. Children should not be subjected to the trauma of seeing adults often in acute stages of psychosis. This is something which can be very stressful for children and has human rights implications," he said.
The Mental Health Commission is currently preparing a list of approved inpatient facilities. Under new legislation, those that fail to meet standards set by the commission face closure or deregistration.
The Department of Health said: "It is accepted that treatment in an adult acute psychiatric unit was considered inappropriate for children."
The Department says it is implementing the findings of a Government-appointed working group in 2000 which recommended the establishment of inpatient psychiatric units for children throughout the country. Outside Dublin and Galway there are no inpatient facilities for under-16s, while nationally there are no specialised inpatient services for 16 to 18-year-olds within the child and adolescent psychiatric service.
The Irish College of Psychiatrists, meanwhile, says that despite rising cases of childhood depression and suicide, only a fraction of children with mental health problems are receiving intervention.
It estimates that there are up to 2,000 children waiting for a psychiatric assessment. There are no official figures on waiting lists available and an internal memo for one health board, obtained under the Freedom of Information Act, shows officials ceased collecting figures "because it was felt to be a demoralising exercise".
Amnesty International's policy officer Ms Fiona Crowley said: "Under the UN Convention on the Rights of the Child, this is a particularly serious human rights infringement."
There are around 20 inpatient beds in Dublin and Galway for children and adolescents with mental health problems, but the Mental Health Commission has said 120 beds are needed nationally.
