You will need:
Container with water
Construction paper
flour
shellac
towel
Have your child dip his hand or feet into the container of water. Shake off any excess water. Place her hand or foot on top of the construction paper, making sure to lift it on and off so it makes a clear water print. Ask her to step onto the towel while you sprinkle flour onto the wet spots on the construction paper. Let the wet flour dry, then spray or paint it with shellac. Try making interesting patterns on the paper but always dip hands or feet into the water and shake them before making a print.
I found this awesome suggestion in the book 365 games toddlers play by Sheila Ellison
I wonder if this could work with a paintbrush and water, having them paint the paper instead? I just love this idea because it isn't nearly as messy as paint.