I think that its really up to the parent because in the end, its thier kid. Don't get me wrong, the annoying little kids with high voices are BAD and ruin it for everyone, but thats no reason to keep all little kids from playing. I do think that adults are more fun to play with though. I'm only 15 and by no means a paragon of xbox live etiquette, but I TRY SO HARD TO BE MATURE AND NOT SWEAR AND I NEVER MAKE RACIAL SLURS. The only time I ever become immature is if I encounter one of the "lets just forget the game and be random" servers,(but its all in good fun) or when I come across one of those little kids or immature jerks who make it thier business to ruin everyone else's fun (looking at you, halo 3). I feel that other teenage jerks on LIVE give '18-and-under' a bad name and so I mostly play with mature adults because they know how to play CoD4 ( read:w/o the noobtube) and I let the small children play with me so long as they show the same level of maturity.