The Cub Scout Pinewood Derby that I saw -- in which the kid is to carve a model car out of a block of wood at home, to race at an event -- they had wisely issued extra kits ahead of time, for those parents who would get a little too enthusiastic about helping Junior, and had separate races among the parents' cars.
Of course, the stakes were much smaller than an award or school admission that potentially makes/breaks your child's brilliant future career.
I had the same thought. :) I don't know what they're doing now. (I saw it when my mom led a Cub Scout pack, decades ago.)
If you wanted to organize some competitions in your city, the track I saw would be easy to build. You might want to design it to break down for storage in someone's garage, and to fit in the back of a couple SUVs. Maybe get city approval to host events as a block party or at a park. Or pre-arrange to donate it to a parish that hosts Scouts and has room to store it and occasionally set it up in their school gym or coffee&donuts hall.
Today, you also have more RC vehicle competitions, and (over-media-ified) generations of battling homebrew robots.
Of course, the stakes were much smaller than an award or school admission that potentially makes/breaks your child's brilliant future career.