My DD is 12 and I was just absentmindedly singing "Frere Jacques" and she said "Oh that song! It used to give me nightmares!"
And I said why? I used to sing it to you all the time!
And she said YES! And it made me think of people drowning...
Apparently she used to hear it and envision a man in bed and then water would rush in and drown him!
What weird fears/thoughts did you or yours have?