We made a mini-marshmallow cannon.
You need a balloon, toilet tissue roll, and a few marshmallows. Tie the mouth of the balloon in a knot. Cut off the bulb end of the balloon. Stretch it and pull over the toilet tissue roll to assemble. If you have a wide rubber band you can add it, but it is optional.
Drop a marshmallow into the cannon; pull back on the balloon, and let go. Great fun!
Now you have a marvelous opportunity for all kinds of learning experiences. Measure distances. Graph results. Calculate and compare.
Actually, at our house, the cousins just had a ton of fun shooting the marshmallows everywhere during BN’s birthday. And eating a few as they did.