Not sure it's a fascination, but I'm guessing every living creature experiences something pre-puberty. The thing is we as society tend focus attention to it and turn something natural into something sexual and right from wrong - including predators who take advantage of it.
I mean, I guess it depends what you consider puberty. I started to notice at 8, couldn't tell you if I was going through early puberty or not, so I answered a firm maybe.
This would be better asked without the loading of the word "sexual". I imagine some people would answer no here because, due to societal pressure, they reframe certain childhood activities as non-sexual. E.g. "Did you ever touch another person's genitals as a child?" may ...