Here's the recipe I used for the finger paint the girls used yesterday.
1/2 cup corn starch and 3 Tablespoons sugar
Mix corn starch and sugar together in saucepan. Add 2 cups cold water to corn starch mixture and mix a little more. Cook over medium heat until mixture begins to clear and thicken (about 5 minutes,) stirring constantly. Remove from stove, cool, and pour into plastic cups. You can add a little food coloring and a drop of detergent to each cup.