Santa Claus also made a special visit ahead of schedule to Ireland to greet a young patients at a special function in Dublin.
However, the real-life benefactor was the supermarket group, Musgrave Super-Valu Centra, which presented €250,000 each to the hospital and the Irish Cancer Society towards the joint development of the new facility at Crumlin.
The money raised for the two charities came from the first-ever Musgrave Triathlon in Cork last September.
More than 500 people including former Olympic athlete Eamonn Coghlan participated in the combined swimming, cycling and running event.
“We are very grateful to accept the funds on behalf of all the children whose lives will be made that little bit easier by the completion of the centre,” said Mr Coghlan who works for the hospital’s Medical and Research Foundation.
“Play is the only normal element in a very abnormal situation in which these children find themselves.”
James Cassidy of the Irish Cancer Society said the provision of such a play centre played a key role in the successful treatment of children.
One beneficiary will be Paul Clarke, 5, from Greystones who has leukaemia.
“The playroom at the hospital is a great distraction for Paul from the business of being injected with needles and taking medicine,” said his mother, Íde.
“He really looks forward to going to the hospital now because there are new toys to play with all the time.”