Indoor Activities for Kids: Homemade Lava Lamps. Vegetable oil, a about of the water bottle, then water. 10 drops of food coloring. Then take a alkaseltzer tab and break it into 4 pieces. Drop one in at a time and wait for each to dissove!
Bottle Bank via Martha Stewart: transform a used plastic bottle into a cute piggy bank. Could use same idea to made little containers for kids to store their collections too (use bottle with wider opening and don't make slot)