just like everything else, they must make the rules for the stupid among us.
my son has been going in the pits since he was 7 because he raced since he was 5 and learned how to safely navigate the pit area. he was always with me back then but by the time he was 10, i had no problem with him moving around by himself.

BUT....that was him and that was then.

NOW i have a 14 year old stepson who is banned from going in the pits cause he just doesnt pay attention.
one night, i caught him wandering down pit lane with his IPOD on and he didnt hear the modified coming up behind him....that was it....he was done......if he wants to go now, he has to sit in the stands.

the problem seems to be that too many parents cant be honest with themselves. be it in the pits, or thinking they have "the next jeff gordon".......and when something happens, they sue the track with the reasoning that the track should be responsible to protect themselves FROM themselves.

with that being said....im not sure if i have an answer. from experience, i have seen both sides of the issue and would probably lean towards NOT allowing kids in the pits. that way it would eliminate the problem and not allow it to be a decision of the parent.