The story of the Children of Lir is one of the best-known tales of Ireland.
This story tells of Lir and his wife Aobh and their four children called Aodh, Fionnghuala, Fiachra and Conn.
Lir's wife died and he married again. His new wife was called Aoife and she became the children's stepmother.
At first she loved them dearly but after a time she grew jealous of their father's affection for them.
One day she bore them away and put them under a spell.
They were turned into four white swans at Lake Derravarragh in County Westmeath.
They remained there for four hundred years.

For the rest of the story see:
http://www.askaboutireland.ie/reading-room/history-heritage/folklore-of-ireland/carlow-folklore/the-story-of-mad-sweeney/the-children-of-lir/