Nutshell: Children of Lir
The four children of King Lir are happy when their father marries again. Aoife, their new stepmother is very kind to them. But in her heart she is jealous of the children and uses her secret magic powers to cast a spell on them, changing them from children into swans.
They spend long years on lonely lakes and frozen seas, until one day the spell is broken and they are human again. Though everyone they loved is long gone, they know they are home at last.