Ah, those were the days! I remember flying over the handlebars on a bike that size when I was about his age... good times...
... and deeply ingrained memories of what 'not to do'.
He's gonna be hooked soon, if he isn't already... good job.
Had my friend's 3-year old daughter sitting on my (not running) bike today, showed her the throttle, and the shiny chrome petrol cap... spreading the '2-wheeled word'. I swear she had a wistful look in her eye as I was riding off!

Have fun teaching your little guy to ride, glad to see him in his safety gear. Yer a good daddy, Hans.