For the youngest— [and the young at heart]
Make vanilla pudding and let it cool.
Divide into three different dishes.
Add different food colorings to each bowl. [red, blue, yellow]
Small children can draw on plain paper to their hearts delight and if they get covered with "paint" they can lick their fingers without concern.
If staining or allergies are a concern, be particular about the coloring used.
[Alternative: Do the same thing with plain yogurt.]
Image credit and thanks to: theyayagirls.com, raisingsparks.com