The Psychiatric Nurses Association (PNA) has said there are just 66 operational beds for Child and Adolescent Mental Health Services (CAMHS) in Ireland.
The annual conference has heard that the health service target was to provide 100 inpatient beds.
In the absence of dedicated CAMHS beds, children end up in acute psychiatric units, or in paediatric wards of general hospitals.
This week the PNA said it has identified only 66 operational beds, although there are 74 in the system.
20 beds are at Merlin Park, Co Galway, 20 beds are at Eist Linn, Co Cork, however only 12 are operational due to a lack of consultant cover, 12 are at St Vincent's in Fairview, Co Dublin and 22 are at Linn Dara Cherry Orchard, Co Dublin.
Earlier the conference heard that the government had failed to deliver on a promise made a decade ago to move to community-based mental health services.
PNA General Secretary Des Kavanagh told the union's annual delegate conference that key elements of policy were 'in disarray' and not even commenced in terms of community services.
The union has published a study of the implementation of the 'A Vision for Change' policy published in 2006 by the then government.
The PNA review was conducted in conjunction with the Royal College of Surgeons in Ireland.
It finds that ten years on, there is a lack of crisis services and high observation beds, a shortage of specialist services for addictions and eating disorders and home-based treatment teams.
Access to day centres and day hospitals is limited.
'Community based mental health services remains a mere aspiration'
Mr Kavanagh told the conference in Cavan that the promise of fully-staffed community-based multi-disciplinary mental health services, as the main method of treatment delivery, remains a mere aspiration across most of the country.
He said that community services are offered on a 9-5 Monday to Friday basis.
The study shows that there has been progress under 'A Vision for Change' in terms of psychiatric hospital closures, developing acute units with general hospitals, strengthened services for older people and suicide prevention programmes.
In response to the PNA criticisms, the HSE said the current mental health budget of €790m provides for direct and indirect staffing of up to 86% of the Vision for Change staffing requirements.
It said that on approval by the Department of Health of 2016 Programme for Government funding of a further €35m, this level can then increase to 90% of Vision for Change staffing levels.
The HSE said it is continuing to use the investment to further develop and enhance mental health services, for all age groups and across all specialties.