My friend gave her son a 49 cc quad motorcycle when he was 18 months. That sucker topped out at 35 miles an hour but she governed it down to about 5 mph. He loved that thing and would always ride it while his dad mowed the lawn. One time dad noticed that DJ would start, then stop. Start, then stop. When the quad would stop, the helmet would bob. Dad ran up and saw he had been riding for hours and was falling asleep in the seat! You can't see it in the video, but when DJ falls he gets a face full of grass!