• Tux Paint

From author's site:

Tux Paint is a free, award-winning drawing program for children ages 3 to 12 (for example, preschool and K-6 in the US, key stages 1 & 2 in the UK). It combines an easy-to-use interface, fun sound effects, and an encouraging cartoon mascot who guides children as they use the program.

Kids are presented with a blank canvas and a variety of drawing tools to help them be creative. (See the full list of features.)