Invent a Board Game
They design the board, write the rules, and then make you play it.
Make it, price it, sell it, count the money.
A whole afternoon project that ends with real arithmetic and a small pile of coins.
Working out cost, price and profit makes arithmetic consequential in a way that no worksheet manages. Speaking to strangers and handling money are also genuinely uncomfortable for many children, and doing it from behind a table makes it manageable.
Own driveway or garden only, with an adult present throughout. Check local rules before selling in a public place. Cover the drink against insects.
Wash everything properly, since food was involved.
They design the board, write the rules, and then make you play it.
A menu, an order pad, and one very slow waiter.
Invent a sandwich, write the recipe, then make someone else follow it exactly.
Seven lolly sticks, two elastic bands, and a pom-pom that goes further than expected.
Two identical piles of bricks, a barrier, and one person giving instructions.
A letter, an envelope, a stamp, and a reply that arrives days later.