Tux Paint, an open source drawing software program for kids. It's a FREE download for Mac or PC. It has a very easy to use interface that includes sound effects that kids love. If your school is watching every penny (like most schools), this is a great drawing program for students of any age. One feature that I think is better than Kidpix is the stamps. They are much more realistic and enlarge much easier and less pixelated. I encourage you to download this and let your students have some fun, then assign them a project or specific drawing to create and see what happens...you may just be surprised!
By the way, they also have free math and typing programs available for download.