I'm also concerned for your son's safety. Is he strapped in? I seriously hurt myself when I was a kid in a dodgem car at a fairground when my face hit the steer

I'm also concerned for your son's safety. Is he strapped in? I seriously hurt myself when I was a kid in a dodgem car at a fairground when my face hit the steering wheel. 7-10km/h may not sound very fast, but trying jogging face-first into a lamppost at that speed and you'll soon change your mind.