Dealing with immodest family members is obviously different where children are involved, but assuming the exposure is infrequent I completely agree with Godefrey.
Something that needs to be said: we have to do everything in our power to give our kids consistent, persistent Catholic friends and acquaintances. When your kids grow up around other Catholics (I don't mean when they see other Catholics for 20 minutes a week after Mass, I mean GROW UP around other Catholics) they develop an in-group identity. What is normal to them is what other Catholic kids and grown ups do. Anything that doesn't fit that mold? Not normal. Weird. Icky. Whatever terms the kids are using. They will naturally see immodesty as something contemptuous if they have peers and other adults reinforcing that standard. I've seen groups of little girls huddle up and mock immodest strangers when they walk by. The reinforcement kids get from their peers is ridiculously formative.
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The older that kids get, the more important this becomes. God made us social creatures by design, not defect. Kids who grow up with a Catholic home will eventually leave that home. Often they leave the home socially before they do physically. If they don't have an existing Catholic social network to inherit, they will have to develop their own or join an existing social network. And if they haven't grown up in a Catholic social environment, chances are they haven't developed the kind of prejudices they should have (prejudice against worldliness).
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