Sekai Meisaku Douwa: Hakuchou no Ouji

Both are very nice fairy tales that they share in common the transformation of people into swans by sorcery and the struggle to lift the curse. Highly recommended for all ages! 

This is also part of the World Children's Classics series along with the aforementioned adaptation of Swan Lake, so the art style and some of the music will be similar or of the same high quality. Similar to World Masterpiece Theatre films (Anne of Green Gables/Heidi/et cetera) & Belle & Sebastian. Bonus: Each film contains the metamorphosis of a girl and her journey through that process. The sound quality of this one is particularly good.