Place shaving cream in the cavities of a muffin tin.
Add a few drops of food coloring or liquid watercolor paint and stir them in using a popsicle stick or a spoon.
Give your child a paintbrush and let them paint the bathroom walls and the inside of the bathtub!
Notes
To prevent staining, use washable liquid watercolors and make sure to clean up the paint right away when you child is done painting. You can also forgo the coloring entirely and keep the shaving cream white.