This isn't a misheard lyric. I heard the right words, but I didn't know what they meant. The Christmas song "Silent Night" contains the lyrics "All is calm, all is bright / 'Round yon virgin mother and child". Everything is calm and bright 'round (around) them.
I heard "'round yon virgin" and imagined that she was round because she was pregnant.
A childhood belief about songs

others believed things like this
- for the longest time every i used to think that Prince's "Raspberry Barret" said "round merry go round"— lin
- I believed my dad when he said that he could see round corners. — Charisma
- I used to believe, the little round bandaids, were to cover bullett holes.Anon
- i thought going to school was getting on the bus and driving round all day until they dropped you off. Anon
- Up until I was nine my uncle told me that the round bales of hay were cow eggs.— Fred
- Thunder was my dead uncle in heaven playing a round of bowling with God.— Mike