I'm posting here for traffic.
When I was a child there were things we weren't allowed to tell anybody outside our family. That meant anybody other than my mother or younger brother.
I can't remember what they all were. There were times when it was explicitly said that "this is a family secret" (can't remember when, just remember it being said) on many occasions). There were times when it wasn't explicitly said, but ironically these were worse things (physical abuse) and we just knew never to talk about that outside the "family" (or even within in fact).
So I grew up thinking it was normal that every family had "family secrets", but now I'm wondering if it is or not.
In my own family (DP & kids) there's nothing I'd tell the kids, or that we do, that they couldn't tell someone about.