In printing, mono means "one of a kind," which is a perfect description of this easy introduction to color mixing, texture, and spontaneity. The only rule here is to have plenty of paper on hand -- because printmaking can be habit-forming.
To start, ask your child to squeeze blobs of washable nontoxic tempera paint onto a cookie sheet.
Lay a large piece of paper on top of the paint and have her smooth it down with the palms of her hands. Lift off the paper, then lay the print flat to dry.
Next, encourage your tot to make designs with her fingers, a cotton swab, or a plastic utensil in the smooth surface of the paint that remains on the cookie sheet. Lift off additional prints on clean sheets of paper. You can add more paint as desired.