There's a smattering of memories, like many others here, of various things when I was a kid. I always played with the girls and learned how to talk like them, run like them, in elementary school. My mom had silk pajamas that I would feel when she wasn't home and imagined wearing them but never dared. I would nearly always be the princess or some other girl character when playing as a kid, would usually choose a female avatar when (rarely) playing video games with my brother...
But a vivid memory is when I was 11. I had a friend a year older who came over often to swim, as many other kids did. But I remember her wearing a bathing suit and seeing her newly grown boobs that probably weren't there the year before. I was fascinated, but not because I was attracted...then that night I had a dream that I was the one in the bathing suit with boobs. I don't remember waking up that morning, but I do remember being in the car that day with my mom. I noticed for the first time that I didn't have the boobs from my dream and exclaimed "oh man!" My mom asked me what that was about and I made up some little excuse I've since forgotten.
But the image of my dream is burned there forever.