Short film of people fighting and only black woman and white girl survive

In 1982, in my elementary class, we saw a short film  on the projector. It was highly inappropriate for our age group, but there you go. Anyway, in the film:

—a group of masked people are shooting it out at what I remember as a large estate type of home

–the audience never sees the faces of anyone there

–it seems to be a war between the people inside the house and those outside

—finally everyone seems to be dead

–the audience has no idea why they are all fighting

–then a little blond white girl starts playing or something

–one of the supposedly dead bodies near her moves

–the person pulls of her mask

–she is a black woman

–she begins stroking the child’s hair very gently, even though they had been on opposite sides before

–the movie ends

This odd, almost post-apocalyptic film has haunted me forever. Any ideas on what it is?

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