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.
Basically coloring designed for children from 4 years. It is necessary to offer the child a few options for the different colorings. It happens that some of them are out of childâ€™s interest, while others will love it. So try to pick up the coloring in accordance with the interests of your children.