Homemade finger paints are nontoxic, washable, and always available.
Source: Martha Stewart Kids, Volume 3 2002
4 tablespoons of sugar
1/2 cup of cornstarch
2 cups of cold water
Stir 4 tablespoons of sugar and 1/2 cup cornstarch together. Add 2 cups of cold water and heat over medium heat until the mixture is thick (the mixture will further thicken as it cools).
Divide into four or more containers, and add food coloring as desired.