Sidewalk Chalk Spray-All you need is Flour, Food coloring, and Warm Water. A tablespoon of flour, 10 drops of food coloring, and about a half cup of warm water. Shake it up in the bottle and let your kid go nuts.
Make the fish out of cardboard or felt, and thread it to the button. For the aquarium, you just need a box. Remove all 8 flaps, then cut windows in the sides and slots for the fish in the top with a box cutter or exacto knife.