That is awesome James, it's always great when your kids or grandkids take an interest. Other than mentioning to him that long sleeves and pants might cause less pain I think you are on the right track. I guess letting him learn about hot scale through direct experience is a good thing too!
Instead of a hook, maybe a support for a campfire set or a tent stake. Ask him what he'd like to make, for himself or his mom or dad. basic things like you said but with lots of fun bends and twists.