Why didn't I think of this before: Giving out Jack Chick Christian tracts to kids along with the candy. Chick even wrote several about Halloween. In the one excerpted below, some teens go out for a harmless night of Halloween fun at the local "haunted house" and one of them ends up getting hit by a car and going to hell (he's the one on the middle right below, wearing the cool Charlie Brown sweater!). But that's what he gets for skipping Sunday school:
So, in summary, tell your youth this Halloween to skip the haunted house and definitely "Don't make the same mistake Timmy made."
If you want more Halloween fun with Jack Chick, see the whole comic here. (By the way, given the Christian nature of the ad above, isn't it a little funny that the girl is dressed as a convict?)