FRS Paint by Numbers is a simple but nice application for kids to color different drawings by following the numbers. The kids are supposed to paint all the identical numbers with the same color to form a beautiful image. The application includes 100 different drawings that display animals, landscapes, flowers, boys, girls, etc. (the trial version only allows you to paint the first five drawings). To paint, the kids must click on a certain color from the palette on the right and then click on the desired portion of the drawing.
All the drawings can be printed, so the kids can paint them with real colors. The application has a very simple user interface for kids and lovely sounds are produced when you click on something. Sadly, the application is not run in full screen, so your kids will have access to your computer.
In short, if you are looking for a simple coloring application for your kids, FRS Paint by Numbers may work for you. However, you may find better similar applications for a bit more money.