We had a very active little boy tonight and so we broke out some props and played with food coloring!
~plate or bowl
~ baking soda
~different colors of food coloring
Put a layer of baking soda onto the plate. Put a few drops of food coloring into the cups then fill with vinegar. Using the eyedropper, pour the vinegar onto the soda. It'll start bubbling and fizzling, L-Pad loved it so much it kept him occupied for about 20-30 minutes (which is definately a triumph in preschooler world), it was easy enough I think to put into the "stuff to do when I can't play with you" pile.)