Why were monstrous children so much a part of 1960s horror films?

Answer 1

I have two words for you: Baby Boom.

The Baby Boom made everyone believe it was okay to just go around and sleep with people, and get pregnant. Movies like The Omen, Rosemary's Baby, and Village of the Damned scared many people into celibacy, believe it or not.

Answer 2

Again, this trend speaks to rise of interest in Horror among young people that occurred during this decade. Children had been occasional victims in classical era horror films, but in the late 1950s they got to be the monsters themselves. I Was A Teenage Werewolf and I Was a Teenage Frankenstein both appeared in 1957, setting off a wave of teenage monster movies. Soon monsters were getting younger and younger (as in Village of the Damned [1960] and Children of the Damned [1964]), while Rosemary’s Baby would appear a few years later in 1968.

Ostensibly, these films allowed angst-ridden teenagers and youngsters the thrill of being socially deviant (if only on screen), even as many of them also functioned as reactionary morality tales about the alleged dangers of youth culture itself (everything from juvenile delinquency to the hippies’ culture of sex, drugs, and rock and roll). This trend perhaps culminates in a series of late 1960s and early 1970s horror films such as Cult of the Damned (1969) and Deathmaster (1972), films that eerily recall the similar murderous excesses of the Manson Family.