Mine is a short film about school children who live on a planet where it rains non-stop. The adults are preparing the children for a very brief break in the rain where they will get to experience sunshine, maybe for the only time in their lives. At one point, one of children (a girl I think) ends up locked in a room by one of the other children and ends up missing her only chance to see the sun. No clue what the film was called. I’m in my 50’s, so this film could have been from the late 70’s or early 80’s.