Swans

In the Irish legend ‘Children of Lir’ (part of the Irish Mythological Cycle), the second wife of the sea god Lir is jealous of the four children he fathered with his first wife. She transforms them into swans, a curse to last 900 years and until a church bell rings, or until they are blessed by a monk. The stepmother is found out and turned into an air demon, and the children, after a long spell as swans, are transformed back into humans — albeit elderly ones who quickly die.
Wow!