Un jeu d'enfants (2001)

Content with two children in an upper class French marriage, a woman finds herself faced with visions of rape, violence and the supernatural. Her husband, a successful businessman also starts experiencing hallucinations in which he often ends up physically hurt. Their babysitter hangs herself and the children begin acting strangely, their sadistic behavior arousing suspicion. It becomes apparent that the children's bodies have been possessed/inhabited by two dirty, old people. (imdb)