I have two children, a boy and a girl (6&2). They both enjoy car rides. My son when he was about 3 he would pretend to wrench with me. Some of the best memories I have with my Dad when I was young was being around cars and tools. I agree with an earlier sentiment to let them explore as much as you can stand. It good time spent with your child or children.
This is him helping me with the start of a restoration of a 74 Corvette.
