Just put a lid on him and tell him not to get out of the car or speak
Rules dictated by the MSA in our sport say 12 years old, but I doubt the event is covered by the MSA rules and regulations so I guess its either up to the circuit or organisers discretion.
If the child's parent or guardian has counter-signed the consent form at signing on I guess there is nothing much anyone can do about it.
Just go make his day Matt