It’s happened to us, sort of.
The very first time we left our daughter with a babysitter who wasn’t a grandmother or aunt, we hired our neighbors 16 year old daughter. We had known her since she was 12, and she seemed like a sweet, responsible, kid. An hour after we left, we got a call from another neighbor that there was a pickup truck in the driveway. We rushed home, and found the babysitter and a guy we’d never met in a state of partial undress in the living room. Our daughter was watching a video in the basement. I’m pretty sure that they were fully undressed when they heard the garage door opening.
My wife had wanted to call the police as soon as we got the call from our neighbor. I was 100% sure what we found was what we would find.
I had a quiet word with the babysitters father. They were quite aware that she was seeing the guy and that they were having sex. Of course we never let her babysit again. But she had lots of babysitting gigs. She worked in the after-school child care program at the local elementary school, and is now a pre-school teacher.
Hopefully the incident represented a one off lapse in judgement.