I don't hate kids, I have a 2 year old. I hate parents who let there vile children go online to ruin everyone elses fun. Your parenting turned him into a douche so you should deal with him, not inflict him on others. There should be an advertising campaign explaining the XBL is not a babysitting service for children so unlikable that there parents won't interact with them.
If they can behave themselves in adult company then I have no problems with children on adult games. If they can't then they shouldn't be there. I would love for games with adult only servers. Unfortunately this can't be policed, look at all of the kids playing M rated games now.
As a guide, if you scream down the mic, TK, sing or play music on the mic, call people noobs or use the word "fail" then you are probably not mature enough for games rated "mature".