You could have him find the roots of the tree it fell from (with multiplicities).

You joke, but it's become a thing for kids to do Rubik's cube. I think it's great for algorithmic thinking. My kid has a whole bunch of classmates who spend their time cubing, going from one algo to a more advanced one, discussing with their friends.

When I took Abstract Algebra 1, I had to sit in the front row because I was too cheap to buy glasses.

I learned about commutators from a guy on the front row who was really good at Rubik's cubes. Concrete examples relatable to your hobbies are great.

I also tried to pay for my lunch by commutating, but the lunch lady wouldn't have it.

A pile of apples (or a stack of one dollar bills) would make a pretty natural introduction to the Peano axioms, and from there the basic mathematical operations.

- A pile without apples is a pile of apples. We call it the empty pile.

- The successor function is to add an apple to the pile. Apply the successor function to the pile of apples and you still have a pile of apples.

- A pile of apples is as large as itself

- If the left pile has as many apples as the right pile, then the right pile also has as many apples as the left pile

- If you have two piles of apples you can add them by checking if the second pile is empty. If it is empty you are done and the result is in the first pile. If not take an apple from the second pile and add it to the first pile. Then check again and repeat

And then you can teach him about the bijection between money and apples. After a little more set theory you can start constructing two piles of apples, one representing what you have one what you have to give away ...

The possibilities are endless.

Not sure if serious or you are the supreme master of deadpan humor. Or both.