[Invisible Bunny King]

Hi all!
Ok, this is my first post, so be gentle with me.
I'm hoping someone can help me identify a movie I saw a long time ago. It was in the early 1980s. All I can remember is the following:
-It started out in an abandoned, multi-floor building, like a school or something.
-one child (10-13 years old) is being chased or followed by a group of children.
-I think they were waring school uniforms
-this group that was following the child were singing or chanting something over and over.
-the child being chased was getting more and more scared and running through the building. Eventually the child is cornered in a room.
-as the group of children approach, the child jumps out of a window, to his/her death.

OK, so that's not helpful, but it is all I can remember. I'm really hoping that someone out there recognizes this and can help me identify this movie.
Thanks in advance.