It is believed that the company The McLoughlin Brothers (en.wikipedia.org/wiki/McLoughlin_Brothers) invented the coloring books. They published a book called The Little Folks' Painting Book in collaboration with Kate Greenaway in 1880.
If while coloring your child goes out of the outline, it will not be so noticeable. When the child sees how cool his result is, it will inspire confidence in him and will be a good stimulus for further work. Good coloring are those with the text in it. The text introduces the kid with the game, the kid will be interesting, while the text will expand its horizons.