If I recall, I was raised going to swap meets as soon as I could walk. I could spot fenders from 100 feet out, had a better angle on the parts on the ground. Swap meets really got me involved in the hobby and love for classic cars.
As far as helping in the shop, I think I was the flash light guy, terrible job for a kid, frustrating for both people, but hey I didnt turn out too bad. Addicted to broncos and classic trucks.
Getting your kid hooked (whether a good "addiction" or not, you decide) early on will help with their willingness to wrench. I got hooked on running hot wheels and retractable car toys that you pull back and let them wind up. Car nut from day 1
Power wheels or rc cars can also help get them to love "driving" which will lead to involvement. They make a bronco power wheels! Buy one and have them assemble their own bronco? Walmart had them for $150 if you can find it