Killer Kid

The killer child works on an assumption the audience cannot switch off: children are to be protected. Invert it and the film gets a reaction that requires almost no effort.

The Bad Seed

The 1956 film had to change its ending because of the Production Code, which would not allow a child murderer to go unpunished, so Rhoda is struck by lightning and the cast take a curtain call in which her mother spanks her. The play it came from had no such problem.

The 1970s wave

The Omen (1976) is the commercial peak and is really a film about a man realising his son is not his. It made an enormous amount of money and its production was followed by a run of accidents that the marketing department made full use of.

Narciso Ibáñez Serrador's Who Can Kill a Child? (1976) is the hard one. A pregnant English couple arrive at a Spanish island where the children have killed all the adults. It opens with eight minutes of documentary footage of children in famines and war, which is a bluntness few films attempt, and then asks its title question literally.

Why it is hard to do

It needs a child who can act, and a director who can shoot around one who cannot. Harvey Stephens was cast as Damien after he attacked Richard Donner at the audition, which Donner had asked him to do.

The modern version

The Babadook (2014) and Hereditary (2018) both use the shape while making the real subject the parent's resentment, which is a more uncomfortable place to put the camera.