As been expressed before, Richard- it's not for everybody. If you feel your child isn't ready for something, I'm sure you wouldn't pursue it.
That being said, with as many kids out there today with the manual dexterity to ride a 50cc bike or drive an enduro kart, I'm sure there are quite a few that will be very good in driving a dragster, especially after an entire year of overseen training. I am always amazed to see, season after season, kids that I remember were in strollers while big brother/sister were racing now in junior cars of their own, strapped in and ready to go in the staging lanes. They all look so tiny- even my son looked swamped in his first car at 8, even though it was a perfect fit. We all, as adults, can't help but think of them as "little kids", but truth is, the kids I see involved in sports seem to mature a bit quicker, grow a bit faster.
EDIT: Eight year old in a Junior Dragster:
EDIT: Five year old in same Junior Dragster:
(The above photos are when we got Emmett's first car on his 8th birthday)
Safety will still be overseen by adults- parents, track officials and other adults in the junior community. It won't be the first time someone will have to be told "don't come back until that's fixed" (and, I might add, then offer to help fix the offense to make the car safe and tech-ready) or "spend a little more time training your driver"... Like I said before- nobody wants to see any of the kids ever get hurt. So everybody spends a lot of time looking out for one another.