The material. Some coloring books offer the ability for the child to simply run over the surface with the pens or crayons provided, and it will turn out to be the right color regardless. Some are more like paint books, and some have magic marker surfaces and come with markers that will not show up on any surface but the specially prepared book pages. Choose the book that best suits you and your child. If you are worried about markings on the walls, then dont select a pack of basic crayons, get something that uses special crayons. If you want your child to exercise their own creativity and not have to fit in the lines or color schemes planned, get basic pages. It is up to you.
So why the fascination, and how can they help you? In the most basic sense, the act of applying colored media to intricate line drawings is a benefit to relaxation and stress reduction. You are able to put the outside world aside for the moment and focus on the art of coloring singularly. Studies have shows that anxiety levels dropped in adults that colored. They did note that simple doodling had no affect on anxiety. The focus on coloring and switching off the brain allows that blocking of anxiety in the moment. Coloring does not have a need for complicated thought processes and like listening to calming music, you are able to get within yourself, isolated from external anxiety, commotion, and distractions.