The Children (1980)

A busload of children has disappeared from the quiet New England town of Ravensback, and Sheriff Billy Hart is on the case. A short while later, he manages to track down the kids, but unfortunately they seem to have been transformed into murderous zombies by a cloud of radioactive gas. How can he stop the killer tykes before they destroy the town?
https://youtu.be/iCybwjhRtA8