system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is it scary when kids sing or laugh or say nursery rhymes in horror movies/games?
gpt
Generally, it's done in a minor key where the tune is altered, so anything can be spoopy when done that way (Have you seen the Teletubby episode in black and white that plays a Joy Division Song over it?).  

Also, one of the early films to do this was Nightmare on Elm Street where kids are jumping rope and singing 1-2 Freddy's coming for you, 3-4, better lock your door.   

In this case, it's contextual.  Freddy Kruger was a child molester and murderer, so it's about dead kids, and the context makes it spoopier.