Ya know, I about as pro-helmet as you get. My kids can't even sit on the gas powered toys without their helmet on. That rule started with my parents when I was a kid and it just stuck.
Now, I've been pretty relaxed concerning the battery powered toys....I mean they only go about 5mph and are made mostly of plastic right? Well, he's turned that thing over twice in the last month so he's probably at the very least going to have to start wearing a bike helmet.