SFX magazine asked Neil Gaiman about the secret of scaring children (in literature, presumably...). He said, "The secret of scaring children is remembering what it was like to be a kid yourself. You need to try to remember what it was you were scared of as a seven or ten-year-old, and how much you enjoyed being scared too."
Hmm, I guess I enjoyed being scared by monster movies, but there were other fears that were no fun at all. I remember one episode of "Alfred Hitchcock Presents" in which someone gets entombed in a drain pipe and nobody realizes it has happened. I had nightmares for weeks after that about being trapped somewhere and suffocated. That one wasn't very enjoyable!
In a lot of Young Adult fiction, scary things like imagining the death of a parent, or the fear of humiliation are also used to good effect.
This goes beyond writing chillers for children--if you look closely at how Stephen King's books work, you'll see that actually what scares as as adults isn't all that different from what scared us as kids.
