In 1946 Bicycle Speedway was invented in England. The kids were racing their bikes around in bomb craters, a ready made banked circle dirt track. The sport grew and there are now tracks and leagues racing all over England , Australia and Poland. The tracks are tiny ovals and they race 4 lap sprints, just like Speedway. These photos of the Findon Skid Kids ( Adelaide , South Australia) are from the early 60s. Kids of all ages race on appropriate size bikes which are single speed free wheelers with Flat Track bars. No Fix wheels here because you cant lay one into a turn without going arse over tit. I don't know if they go on to become Speedway riders but I bet their racecraft is fine honed after hundreds of heat races. Looks like fun to me.
www.cyclespeedway.asn.au