When it comes to visuals, kids prefer colors, colors and colors. The colorful and action oriented pictures play a very important role when it comes to illustrations created for children books. Still, the children in different age group need different treatment, when it comes to presenting them with the storybooks.
Books which is read by the parents with the kids beside, needs a lot of pictures/illustrations as the kid will be interested only and only the picture. He will relate the entire story based on the illustrations only, so it is very important to add a lot of illustrations to the small children story books. The child, who is learning to read, also shows interest if he finds very small interesting words. So adding the illustrations and relating them with small words attract the children around 5 to 7 years old. Children 10 and above can do with the less illustrations, but importance of illustrations will never be reduced, as visuals can always impress the human eye of any age.