Make sure you use origami paper, which you can find in most craft stores (or probably Amazon <eye roll>) to start out. The right paper makes it easier when learning; later you can use whatever crap paper is at hand (bulletins, for instance). You should be able to find folding instructions on YouTube, or even specific phone/tablet apps.

Also fun: paper “balloons” (really folded boxes) that can be used for impromptu finger-soccer matches and then squashed flat quickly if a parent/spouse/responsible adult suddenly takes an interest.