Fill your ice cube trays with water, adding a drop of food coloring to each section. When frozen, these can be popped out and put in bath water. They’ll have fun “chasing” them around in the tub and trying to grab them before they melt.
Another pinner: "This kept my 2 year busy for an entire hour and my 4 year old busy for 2 hours! YAY! Drop vinegar tinted with food coloring onto a pan filled with baking soda. Sheer minutes of colorful fizzy fun!"