Missing cartoon movie....?

I used to watch this cartoon movie when I was younger. It's about this two siblings, an older girl and a younger boy who were playing in the woods. Then the two kids stumble upon a feast prepared by the fairies(?) who were living in the woods. The boy who was really hungry ate one of the pastries on the table, unknown to them that there is policy that any outsider who eats anything would have to stay in the woods with them forever. I don't know what happens next but at the end the fairy King marries the sibling's aunt. Thank you! :D