1. Cut small pieces of paper. Decorate the paper.
2. Either roll the paper around the straw (not too tight) and tape it OR just fold the paper in half lengthwise and tape it.
3. Fold down the top edge of the paper (to create a seal) and tape it.
4. Put the rocket on the straw.
5. Blow through the straw to launch the rocket.
The simplest version is shown on Simple Play Ideas. Here are the photos, but go to their site for the detailed instructions.
You can also check out: https://toddlerapproved.com/2014/06/tinkerlab-hands-on-guide-for-little.html
One of our teachers built this one based on the project shown at: https://frugalfun4boys.com/make-easy-straw-rockets/
There’s also a slightly different method, where you use a wider straw as the rocket base, with a decorative rocket attached. See that one here: https://inspirationlaboratories.com/make-straw-rockets/
It’s fun to design different rockets and decorate them in different ways. Once they’re built, you can try challenges like: which can fly the highest, which can fly the furthest, and which one is most accurate at hitting a target or flying through a hoop.