It’s been a year in development, but the latest version of Tux Paint (0.9.15) is available on SourceForge. It’s a lot of fun for little kids who are just learning to use the mouse interface (usually around 3 or so, depending on your proclivities), as it incorporates all the usual paint tools, plus cute stamps, sound effects, and a little penguin mascot to giude your kids through the program. Best of all, it’s available for Windows, Mac, and some *NIX and Linux distros. Plus, it works on slower machines and thin-client computers for those schools that can’t afford the latest hardware. Nifty!
TuxPaint, an open-source drawing program for kids