TuxPaint - [Open Source] "is a free, award-winning drawing program for children ages 3 to 12 (for example, preschool and K-6). It combines an easy-to-use interface, fun sound effects, and an encouraging cartoon mascot who guides children as they use the program."
It opens with a blank canvas with tools along the edges. Besides the expected brush, line, color, text tools there is also a rubber stamp. More fonts and stamps can be added, even making your own! Tons of "magic" effects.
Enjoy their Gallery of pictures drawn by children (and Adults) around the world!