The Believers (1987)

Widowed police psychiatrist (Martin Sheen) and his young son (Harley Cross) move to NYC and get involved with a cult that believes in human sacrifices--small children especially.
Exceptionally well-made, deadly serious horror film is not for everybody. It's way too long, has some very disturbing scenes (quick closeups of a dead child's mutilated body; animal sacrifice) and it's serious tone can wear one down. Still, it's a complex, one of a kind horror film. Name all the major studio films that deal with cults, voodoo and children sacrifices--there aren't any! It's surprising this even got made.