We wound up becoming pretty good friends with one of my wife’s law school professors, whose younger child was in the same school (and Sunday school) class as our older child for many years. (The two of them are still really close.) It took my wife awhile to get used to dealing with him as a peer, not someone with power over her.
Another parent in the same class had been a counselor at the sleepaway camp I went to when I was nine. She was actually the girlfriend of my college-student bunk counselor that summer; we were doubtless familiar with one another then, though neither of us remembered it. We had known each other for 7-8 years before we figured out that highly unlikely connection.