I remember seeing an animated movie about fifteen to twenty years ago. I can only remember vague images and details from it but I'll give it a try. It dealt with 2 or more young children who somehow came to a castle/cave by capture or some other design. This place was filled with small(child size) blue goblin type creatures with white hair. Skip to the end and the children do something to allow sunlight into this place and all the creatures turn into children, presumably captured and transformed. Does this ring a bell with any of you?