Make a Shadow Theatre
A cardboard frame, a white sheet, a lamp, and a proper show.
They design the board, write the rules, and then make you play it.
A long project that fills a whole wet afternoon and ends with something they can actually use.
The valuable part is the second playthrough. Discovering that a rule they wrote makes the game unwinnable, and then fixing it, is systems thinking and revision in one. Writing rules clearly enough for someone else to follow is also demanding, precise writing.
None needed.
Keep it. Games they made themselves get played far more than you expect.
A cardboard frame, a white sheet, a lamp, and a proper show.
Every blanket in the house, one afternoon, one secret headquarters.
A big box, some tape, and no instructions whatsoever.
Fold a page into six boxes and tell a whole story inside them.
One sheet of paper, eight folds, and endless silly predictions.
Ten words, one code, and a conversation nobody else can follow.