Metsluiged (1987)

Once upon a time, a King had eleven sons and one daughter. When his wife, the Queen, died, the King remarried. The new wife and the children's stepmother looks beautiful on the outside, but actually she's an evil witch. She sends the young princess Eliise to live in the village as an ordinary peasant girl and turns all the princes into wild swans. The princes are stuck being swans all day long and only at night can they regain their true form. When Eliise is 15 years old, she learns about the fate of her brothers and now she must overcome the obstacles put in her way by her stepmother in order to release her brothers from the spell.