It offers you a good bunch of photos and pictures divided into areas. Each area has a number and each number means a color. Your goal, or your children's goal is to color the picture according to the pattern.
The Monalisa, the statue of liberty,... color important masterpieces, so they'll have fun while they learn something.
Search for the numebr and the color and try to color the picture. You'll feel like Leonardo da Vinci.
If you want your children to have fun coloring using the computer, SegPlayPC can be a good way to get used to the mouse.