The Boy Who Became a Cupboard (1989)

Sinopsis

Parents from around the world hold a congress to discuss how to deal with their misbehaving children. All parents come together — only one set is missing, the parents of Sylvester, the best boy in the world. The congress decides to go see him so he can lead the other children by example. Sylvester is truly an exceptional child, but his "being good at all times and under all circumstances" somewhat gets out of hand.