Children, The (1980)

aka: The Children Of Ravensback

A busload of children has disappeared from the quiet New England town of Ravensback, and Sheriff Billy Hart (Gil Rogers) is on the case. A short while later, he manages to track down the kids. Unfortunately they seem to have been transformed into murderous zombies by a cloud of radioactive gas from a nuclear plant leak. Also stars Martin Shakar and Gale Garnett.