Those aged 4-18 who have Leap cards can travel for free on public transport for the next two weeks.
Dublin Bus, Luas and Dart journeys and commuter rail short hops will be free to children and teens provided their cards contain at least 1 cent of credit.
Some Bus Éireann services will also be free, including in Dublin and surrounding counties and in Cork, Limerick, Galway and Waterford cities.
The Ashbourne Connect will also be part of the scheme, although Expressway services and Airlink will not.
For those who do not have a Leap card a limited stock is available free for those aged 4-15 years at Dublin Bus head office on O’Connell Street, as well as at the city’s three main train stations and the main bus stations in Galway, Limerick and Waterford.
Minister for Transport Shane Ross said it was a "fantastic" initiative from the National Transport Authority, which he hoped would encourage lots of families with young children to avail of public transport for their summer outings.