Your child’s next bath very well might be his very favorite bathtime ever. My daughter and I just had so much fun with an idea from a book called “Prime Time Together with Kids.” Maybe you’ll want to try it too!
Materials:
- muffin tin (or several cups)
- food coloring
- shaving cream
- paintbrush (optional)
Instructions
The paint is very simple to make! All you need to do is fill the muffin tin or cups with shaving cream. Squirt in some food coloring of your choice and mix it up. 
Paint away! It will easily wash off your tub and tiles – assuming your child lets you!
SOURCE:http://www.pbs.org/parents/crafts-for-kids/bathtub-paint-for-kids/