Here's an idea for bathtime-adventures!
Make up a tray of colored ice cubes... just fill the tray with water (don't fill all the way or your colors will run together) and then add a few drops of food coloring to each one. Stir up a bit and pop it in the freezer. Stick a few cubes in the tub with your kids and they will have a blast chasing them around the tub, watching the bath water change colors as the cubes melt!
Super easy and squeaky-clean fun!