Just a quick post to show you a website I stumbled across recently.
http://www.jacksonpollock.org/ is designed by artist Miltos Manetas. It is inspired by the work of Jackson Pollock, in case you hadn't guessed, and works very nicely as a touchscreen game or, even better, on a whiteboard. The kids I've tried it with seem to enjoy the instant and colourful effect of touching the screen. Nice and simple, but effective!
I'll leave you to play with it, but if you want to print what you've created, I suggest pressing ALT then F then V, which will take you to the print preview without adding any more paint to your work. And if you're using IE7 you can adjust the size and shape as the image tends to get stretched out when printed.