KPaul,
I started both of my daughters on dirt bikes early (5 and 7) a few years ago. 5 was a bit young, but by the time she was six, we did a 9 day camping/dirtbike riding in the U.P. of Michigan.
If you want to get your kids to be safe, responsible drivers when they turn 16, get them on a dirt bike early. They'll understand spatial awareness, not panic when a vehicle slides, and know that if they want to hot rod, they do it off of the street. It is SO much better than driver's ed.
I have many frightening statistics about teen drivers. If you want your kid to be safe, teach them early. Buy your daughter a dirt bike, and buy yourself one, too. Spend time alone with her in the woods. Its the best thing on earth. It will also make you a better street rider for the very same reasons. Maybe even help you smoke Sean on the track.....
Well, I wouldn't go that far.