There is a way to lock out all sorts of details from people seeing-not only "ALL" people, but any single fb user as well.
I know-because I used it.
Furthermore-you could probably have one of your kids show you how to do precisely that-before anything is on there at all.
Then you can play with the settings and get a feel for it before you make a decision.
I understand your "waffle".
I opted for being completely upfront and open on my facebook. The large majority of people I talk to on fb are my poly-peeps, so I didnt want to pretend to be something else.
At the same time, my husbands' nieces and nephews and cousins, aunts/uncles etc are all on there-and I don't feel like it's right for me to be the "educator" of other people's children.....
Ultimately-I decided that if their parents weren't monitoring their internet use-that was their problem. I don't add them as friends-but beyond that, they have parents, I have my own kids to keep track of.
In your case-you have the battle of custody-that's a nasty place for alternative lifestyles to get drug into.