Coloring helps the child to learn how to control the scale of his hand. Please note that when the baby is just started to draw he does not monitor the boundaries of the sheet, and the picture is not painted on the outlines, and even beyond.
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.