The younger the child, the larger and easier the drawing is. The outlines are indicated by a thick line from 2 to 4 mm, so that for the child it is easier to stay within the contours.
There is another advantage of colorings for adults. Most of them are very nice and include impressive black-and-white contours that can be turned into a work of art. Imagine the feeling of satisfaction that you get when you have finished drawing and will be able to appreciate the beauty of the masterpiece created by you personally.