Materials question

Fin was asking me for a battery the other day.

Says I, "Batteries aren't really a toy, what do you need it for?"

After a crying jag that I wouldn't let him have a battery to play with he finally calmed down and said that he wanted to make a blueberry picker so we'd be ready for blueberry season. He drew me some plans and I said,

"Well, why don't we gather the other materials and put the battery in last?" I was thinking that this would all be made of cardboard and duct tape - his main building materials.

He pointed to the body of his machine and said, "Wait, do we even HAVE steel?"

So hard not to crack up. Sure kid, I've got a whole pile of scrap in the garage. Just make sure you have a welding helmet on.