What's the craziest thing you believed as a child?
Not necessarily gaps in your education/experiences (because we've already covered that), but perhaps things your parents told you (beyond the typical Santa Claus, Easter Bunny, Tooth Fairy crap) that weren't true, or even stuff you made up in your own head.
For example: Up until about the 2nd grade I had convinced myself that the teachers lived at school. I thought they all had a secret button in their rooms somewhere that would turn the classroom into their apartment. Usually (in my head) the desk turned into their bed, one wall had a TV in it, our desks magically turned into a couch... stuff like that.