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There's no way use could use the same kart he would use a midget kart with a comer 80cc pull start motor and you would need a rotax 125cc water cooled on a senior chassis.you could run a clubman 100cc but still the young fella can't drive it

I would also give the thumbs up for carting over motocross when it comes to my child.
I would say that he has a better chance breaking a arm when riding his BMX bike like a maniac than racing a cart. They are very tight gripped on the road surface and will take a crazy move to make it fall over, if it even is possible. Find out the classes, maybe you can share one cart. He drives junior class and you drive senior class. Or something like that.

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Like all racing people get hurt.but in saying that I raced karts for 7years and never got an injury.its just 1 of those things

As with all forms of motorsport there is a risk.
Heaps less pain than bikes. A spin or a bump is going to hurt a lot less than going over handle bars.
#OOPS# my wife let me and my son race and came away with us to meetings.So it has to be safe.
Look up Oakleigh go kart club in your area and have a look at a club day (usually last Sunday of the month and then thank me ).

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Build an A6 powered cart or A series powered Formula Ford :)

Seriously drifting if possible at his age could be cheap with an R31

Why dont you both give racing Karts a go.
They are a pretty serious form of motorsport.You can both race at one venue at the same weekend use the same tools etc.
Later on join a car club and go from there.
That was about what we did.
You learn what you want in the setup of a vehicle plus karts have to be the best way of developing driving skills.