My hubby and I kind of feel the same way about some of our friends and their kids. We thank God that they are not ours, but we do try and get together as much as we can with them and their kids. My hubby and the other Dad have know each other since my hubby was born and are still friends. We want our kids to have that same life long friendship with them also. Their kids are not horrible kids by any means, just disciplined differently than ours. On our turf, our rules go. And if I have to discuss those rules with my friends kids, then I do so like they are an adult. Same goes with warnings, first time is a warning, if we have to talk about it again, you lose the toy for example. Time outs as well. Now, on their turf, I just explain to my little one that we don't do that at home and we are not going to do that anywhere else. Mommy and Daddy don't allow it no matter where we are, so you need to be nice and find something else to play with, for example. We use, "nice" in front of everything...nice hands, nice feet, nice toys.
It is not worth loosing friends over because the good ones are few and far between.
Hope this helps!