I think the biggest problem people have when drawing with crayons is that they regress to being five years old again. They hold the crayon like they're coloring again, instead of applying it like a fine art medium. Another problem is that many people want to make it perform like colored pencils. While similar in application, they are quite different. You should not use crayons and expect them to behave like colored pencils. You'll be setting yourself up for disappointment.
In fact, taking a crayon or colored pencil to paper is a therapy method that dates back to the early 20th century _ though it seems people are just starting to rediscover its benefits. So how exactly does something as simple and seemingly childlike as filling in the lines lend itself to combating adult amounts of stress?