What is the best Facebook security setting to keep kids out of "grown up" postings?

Hi! I have a Facebook account, and lately the children of my friends and family are starting to get accounts. Some are younger than they should be, but they are out there. And they are friending me. I honestly feel a little strange about “friending” a child AND I definitely don’t want them to see some of the “adult” things I post. Nothing “dicey,” but pix of me at a party having drinks with their parents (or maybe doing something silly) just doesn’t seem appropriate. But at the same time, I have known most of these kids since birth and feel like I “should” friend them.

Of the few I have friended, I have categorized as “kids” in FB. Now I need to try and figure out how to permission that group. Can you make a recommendation?

Thanks!