Does anybody know the movie to fit this description?

I have been trying to find a movie, and all I know is roughly the end. Does anyone know a film that has a monster that changes people or children into a stone figure or something of that sort, and at the end the monster and all the children's parents are in a park of some sort and the parents sing a song or melody and that kills the monster; maybe green slime explodes from him when the parents kill him and all the kids are brought back to life. If anybody could tell me what this film is, my mind would be put at rest because iv'e been trying to figure it out for a very long time now.