Collect everything you need for the experiment: one tall, clear container (a glass vase, large jar, or clear plastic bottle works great), 5 small cups or bowls, water, white sugar, 5 colors of food coloring (red, orange, yellow, green, blue or purple), measuring spoons, a spoon for stirring, and a medicine dropper or turkey baster for layering (optional but helpful). You'll also need a flat workspace covered with newspaper or a tray in case of spills—this can get messy. Set everything out so your child can see all the materials. Explain that you're going to make a rainbow in a bottle by stacking different colored liquids on top of each other, and they won't mix because of something called density. Don't explain density yet—let the experiment teach it.

Now you'll make 5 colored sugar solutions, each with a different amount of sugar to create different densities. Fill each of the 5 cups with 2 tablespoons of water. Add food coloring to each cup (red, orange, yellow, green, blue) and stir—use enough color to make them vibrant. Now add sugar in increasing amounts: Cup 1 (red): no sugar. Cup 2 (orange): 1 tablespoon sugar, stir until dissolved. Cup 3 (yellow): 2 tablespoons sugar, stir. Cup 4 (green): 3 tablespoons sugar, stir. Cup 5 (blue): 4 tablespoons sugar, stir. The more sugar in the water, the denser the liquid. Make sure the sugar is fully dissolved in each cup before moving on—this is critical for the experiment to work. Let your child do the measuring, pouring, and stirring with supervision.

Now for the magic! You'll pour the liquids into the clear container one at a time, starting with the densest (most sugar) at the bottom. Start with Cup 5 (blue, 4 tablespoons sugar)—pour it into the bottom of the container. Next, slowly add Cup 4 (green, 3 tablespoons)—pour very slowly down the side of the container or use a medicine dropper/turkey baster to add it gently on top of the blue. You should see a distinct layer forming. Continue with Cup 3 (yellow, 2 tablespoons), Cup 2 (orange, 1 tablespoon), and finally Cup 1 (red, no sugar) on top. The key is pouring slowly and carefully—if you dump it in fast, the layers will mix. Use the side of the container or a spoon held inside to diffuse the pour. When done correctly, you'll have a beautiful rainbow bottle with distinct colored layers that don't mix.

Now that the rainbow bottle is complete, talk about the science. Ask your child: 'Why do you think the colors stayed separate instead of mixing?' Explain the concept of density: density is how much stuff (molecules, particles) is packed into a space. The blue liquid at the bottom has the most sugar dissolved in it, so it's the most packed—the densest. The red liquid at the top has no sugar, so it's the least dense. Dense liquids sink to the bottom; less dense liquids float on top. That's why oil floats on water (oil is less dense) and rocks sink in water (rocks are denser). Use analogies: 'Imagine a crowded elevator versus an empty one—the crowded one is denser.' Let your child look closely at the layers and see if they can spot any mixing where densities are similar.

Let your child examine the rainbow bottle closely. Can they see any places where colors blend slightly? That's where densities were similar. Gently tilt the bottle—do the layers hold or start to mix? Set the bottle somewhere visible (a windowsill, shelf, or table) to admire. Over the next few hours or days, check if the layers stay separate or slowly mix—this can happen as temperatures change or the bottle gets jostled. Discuss doing more density experiments: making lava lamps with oil and water, testing which objects float or sink, or creating layered drinks. Celebrate that your child just did real science—they formed a hypothesis (will the liquids layer?), conducted an experiment, observed results, and learned a physics concept. That's the scientific method in action, all with sugar and food coloring.