Science Day: This is really a really cool simple experiment! Learn how density affects submerged objects.
What you will need: A bucket of water filled half way. Two cans of carbonated soda, same size and brand, but one regular, one diet.
Have your child drop the regular soda in the water first. Does it sink? Yes. Have your child now drop the diet soda in the pail of water. Does it sink? No! It pops back up and floats because the density of the diet soda is less than the regular one.