My son was driving a MF8H when he was 7 or 8... I built a new handle on the parking brake lever so he could (in one motion) take it out of "gear" and hit the brakes.
I walked beside him & watched the first lap or two. Only time he got into trouble (after he learned Dad was nuts enough to walk in front of him so he'd better keep 1 hand on the new handle) was when he messed with the throttle & it stalled. End of riding for the day.
I think part of the reason there are so many BAD drivers out there today, is they were never taught basic machine safety at an age that they were young enough to care.