Garda Vetting is required for any person carrying out work or activity, a necessary and regular part of which consists mainly of the person having access to, or contact with, children or vulnerable adults. The requirement does not apply where a person gives assistance on an occasional basis at a school, sports or community event or activity, other than where such assistance includes the coaching, mentoring, counselling, teaching or training of children or vulnerable persons. If you require Garda Vetting, then the application should be done through the institution where you will work with children. They will provide you with a customized invitation form to start the process.
You might find these Garda Vetting information pages useful: UCC, UCD, Limerick University, NUI Galway, Maynooth University.