Ever since we colored our Easter eggs using a mixture of baking soda, food coloring and vinegar Sweet Girl has been dying to do them again. And since I didn't really feel like dying more eggs (such a mess!) I decided to just let her play around with a big dish of baking soda and some food coloring mixed with vinegar.
She used eye droppers to drop some of the food coloring/vinegar mix into the baking soda pan. She LOVED watching the baking soda foam up....and the colors were great.
She played with this until all the cups of food coloring were empty (note to self....use larger cups next time!!)