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Karting would be the best bang for your buck racing. Cheap enough and doesn't take up much space. Its a great platform to hone your skills.

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youngest age to apply for a cams license is 12 yo as far as i know.
I would start with joining a cams approved car club followed by a cams license..

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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.

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

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

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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 ).