The Mental Health Commission says it is totally unacceptable that children are still being admitted to adult mental health units.
The Commission has identified 12 areas of high-risk non-compliance at three of its approved centres in Waterford, Clare and Cork.
The Commission said eight children have been admitted to the Department of Psychiatry at University Hospital Waterford since last July.
This is despite its lack of age-appropriate facilities, while inspectors also noted that not all staff involved in the care of children had training in Children First.
John Farrelly, the Chief Executive of the Mental Health Commission says this is "totally unacceptable", but still a common feature of mental health care practice in Ireland.
There were also issues surrounding the hospitals use of CCTV, staffing and use of physical restraints.
Meanwhile, the Acute Psychiatric Unit at Ennis Hospital, Co Clare had three high-risk ratings for personal property and possessions, individual care planning and general health.
Inspectors said that medication management procedures at Owenacurra Centre, Midleton, Co Cork were not consistently safe.
The medication trolley was not locked at all times, while drugs due to be returned to the pharmacy were seen as being stored in an open box.
Inspectors also said that there were not enough showers for the 21 residents at the centre.