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.

In 3-4 year old kids are more confident in coloring. They're not trying to draw freely, and act within the circuit, trying to repeat the figure bends.

Little Red Riding Hood Coloring Pages