I remember seeing this movie in the early 80’s. There is a group of kids that live on Venus (I think). It always rains. They are preparing for a momentary break I the rain when the sun will come out. It is the first time most of the kids will see the sun, except for a new girl who has seen it before. For some reason they lock the girl in the room, out of jealousy maybe, and the sun comes out. They forget about her and she misses the whole thing.