The Bath House.

Set in the WWII era, the story tells of a boy in a small village who befriends three girls around his age. One day he discovers a young couple sneaking into an old and cracked bathing shack and decides to alert his new friends. When the kids join up at the shack, the eldest girl comes up with the idea to lock the couple inside, threatening not to let them out until they "do it" and allow the kids to watch from the outside. And so begins the psychological warfare...