This mini ocean made major waves with our kid testers, who loved to send the shells, sand, and water tossing and tumbling. The project starts with a clean plastic bottle (ours is an 18-ounce beverage container). Pour in 1/4 cup of sand and add a handful of small shells (we used ten). Mix a drop of green and a drop of blue food coloring into 6 cups of water, then use the tinted water to fill the bottle halfway. Add a pinch of silver glitter. Fill the rest of the bottle with mineral or baby oil, leaving as little air space at the top as possible. Run a line of hot glue around the inside of the bottle cap, then quickly screw on the cap to create a spill-proof seal.