Coloring in a picture will command your child's full attention, as they concentrate on completing their work, and having the finished product show that they have done their best. This is a welcome assistance for parents who struggle to provide their children with experiences that will captivate their attention, only to find that their little minds and bodies start wandering after only a short time. So as a parent, you gain a short respite as your child works on their coloring page, your child gets to participate in a fun activity that teaches them as well. Which leads me to the next point.
Another advantage of coloring pages is that they provide your child with the chance to strengthen their hand eye coordination, as they learn to color in the lines. This skill will develop gradually as they go from struggling to stay inside the lines, to perfecting this fine motor activity.