Tux Paint is the best painting program ever. It is free, flexible, loud, incredibly fun, and most of all, it can make some pretty nice pictures.
Kids love using it. The stamps offer a large variety of pictures, the drawing tools are very flexible, and the magic tools can add some great effects. And the eraser! I mean, all kids painting programs should have such an amazing loud and large eraser.
Use Tux Paint! It is free!
The Grade 2's were using it today, and we saw some awesome pictures.