This was so embarrassing... We were at a family reunion, and there was a "family magazine" where relatives were listed, along with their birthdate, marriage date, and then the birthdates of their children etc.
My dear cousin Mary (6 years old, mathematically smart, has a 1-year-old little brother who was born 2 months premature) was reading the magazine. She then asked our great-uncle, a very respectable 70-year-old reverend, "Uncle Tim, did Uncle John (Tim's son, about 45 years old) have to stay in the hospital glass bassinet very long when he was born?" Tim was naturally very puzzled as to why Mary would ask this. "You see, it seems that John was born only 6 months after you and Aunt Matilda got married, so he must've been far too small to come home straight from the hospital? Right?"