In a few years they'll be playing Call of Duty: Iraqi Freedom, may as well let them get acclimated now.
Or you can set your alliance to invite only or closed. Though if you're trying to get new people, then that means you'll have to -gasp!- deal with people, and all the wonderful and horrible things that may entail. Kids can't wear oven mitts and bicycle helmets everywhere all their lives.
The online world and it's anonymity does invite its share of vulgarities but you may have to question just why your alliance is receiving so many of them at some point. I've been playing the game for over two years in myriad groups and I can't say I've noticed too many torrents of obscenities from random folks.