These little submarines are made from the two-piece plastic eggs that turn up in every craft drawer, and they cost almost nothing to put together. You draw on some portholes, add a straw periscope, drop a few coins inside for ballast, and set them loose in a bowl of water. There is a bit of real science hiding in them, because how much you weight each one decides whether it floats, hovers, or sinks. Ages 3 to 6.
Making the submarines
Start with the body. Draw a row of round portholes and a hatch on each plastic egg with a permanent marker. Different colors for each submarine make them easy to tell apart later, and it is a nice job to hand to a child who likes to decorate.
Next comes the ballast, which is where the science creeps in. Open the egg, drop a few coins into the bottom half, and close it again. The coins act as weight, the same way a real submarine takes on water to dive. A little experimenting shows that more coins make the submarine sit lower, and too many send it straight to the bottom.
Last is the periscope. Push a bendy straw through a small hole in the top of the egg and seal around it with a blob of playdough or a wrap of tape so it stays put. The straw also gives a child something to hold while they push the submarine under.
Setting up the ocean
A clear glass bowl makes the best ocean, because you can watch the submarines from the side as they rise and dive. Lay a seabed of colored rice along the bottom, scatter a few glass pebbles over it, and fill the bowl with water. It looks the part, and the clear sides are what turn a bit of bath play into something you can actually observe.
Diving and surfacing
Now the playing begins. Push a submarine under and let it bob back up, add or remove coins to change how it sits, and race two of them from one side of the bowl to the other. The talk that comes with it is the good part: why this one floats higher, what happens if we add another coin, where the bubbles come from when it goes under. It is water play and a first lesson in floating and sinking at the same time.
For another colorful, hands-on activity on a quieter day, our color surprise playdough hides a blob of paint inside white dough for a squashing surprise. And to carry the underwater theme onto paper, our free mermaid coloring pages keep the ocean going once the water is tipped out.