The best thing you can do is get to know the parents of the children they're hanging around. That will give you a good idea of the kind of children you're dealing with in the first place. I agree that you need to be very cautious on who you let them hang out with. One thing I would recommend is to look into the temperament of your children, as it will give you an idea how they will react in certain situations.
Like, I know one of my daughters is pretty much a pure sanguine, and she is a major follower... really is impressionable, and can be defiant at times if she doesn't agree with me on something (like the pants issue is really getting on my nerves already :faint:). I make her wear dresses or skirts, and she can't leave the house until she changes, and I won't let her wear immodest clothes at all. Sometimes, she'll fight me, although, I've been taking her shopping myself, to show her how difficult it is to find things. It's getting better though. She recognizes when someone's dressed immodestly, and will quip when she sees it. The pants thing, however, irritates me. Her grandmother gave all kinds of excuses as to why she should be able to wear pants (i.e. we live in a cold climate, et cetera, you know, the usual lame arguments). I'd make her wear a skirt over them, but she got into the habit, since her grandmother didn't reinforce my wishes, of wearing them without one. I gotta buy some more legwarmers that fit her...
Garage sales...
Oh, and I absolutely forbid Disney movies (but my oh so wise mother in law :cussing: overrode my wishes and let them secretly watch the filth at her house, and I didn't find out about it until months after the fact.) Then you hear "Grandma let us do it." It's like "WTH..." The truly surprising thing is that my mother in law goes to daily (traditional) Mass, and says the daily rosary, and still, does this kind of thing. It's frigging irritating!
I have an indult (traditional) Catholic sister in law who regularly wears pants, too, and that's confusing to my daughter as well. You just tell them what's right, and hope that they make an impression if the people you're talking about are family.
I don't have a lot of outside acquaintances, because I have a very few close friends, and I really watch who my children are hanging around. More often than not, I get comments as to how well the children behave themselves outside the house (and they're certainly not very obedient around here.

). But the parents and such are mostly edified by their behavior. Occasionally I'll get a comment on my son and how he is mean, but that's usually when he's severely outnumbered by girls

.