"The golden age" of coloring books is believed to be 1960-s, because almost all characters were depicted in them, as well as some products (like Planter Peanuts or Campbell Soup)
Images for older children may already contain small parts, complex narrative compositions with greater color palette. The outline is more subtle. These can be supplemented with coloring tasks. For example, to write the missing word, or paste a sticker, finish drawing, connect the dots.