K.D.
I'm in a similar situation, although my children are not yet old enough to really understand anything or have pressure from other kids/parents. Having been raised in a non-active LDS family, my father feels it's his "responsability" to update the church on my whereabouts, but I've found that when they come knocking, I just say, as politely as possible, that I appreciate them stopping by, but I am not interested in the church and thank them for coming. They usually just say, "Okay" and leave (sometimes starting to close your door really gives them the hint or just don't invite them in). Occasionally I'll get someone who wants says something like, "Do you want to talk about it?" and I just say, "No. I'm perfectly happy with my choice. Thanks, though." And if they are offended, that's their problem, not yours.
And my feeling is, if they ostracize you or your sons because of your choice, that certainly isn't very Christian of them and do you really want your boys playing with their kids who's parents are raising them to be so closed minded? I'm sure your boys will find plenty of other kids (both Mormon and not) who they can be good friends with, just give it some time.
Good luck.