The other day my daughter made an observation. She said: "It seems like there are more boys having adventures in books than girls having adventures." (Or something to that effect). For what it's worth, she made this observation as we were starting the fourth Harry Potter book together. She is seven, and just finished first grade.
Caught off-guard - I was not expecting her to notice this so soon - I told her what I see as the simplest explanation. That people at least perceive that boys are less willing to read books about girls than vice versa, leading authors and publishers seeking the widest readership to write books featuring boys. My daughter accepted this as a logical explanation and we moved on. But I was left with a mix of pride that she's observant enough to figure this out and sadness that it's there for her to see, so soon.
I don't think that this one will be anyone's favorite of my daughter's milestones on the path to literacy. Certainly it is not mine. But I did think that it was worth sharing with you all as a data point. Coincidentally, I just ran across a BBC News piece about the new UK Children's Laureate, Lauren Child, in which Child brings up this exact issue.
Of course my daughter is lucky because I am more equipped than most to find her books that DO feature girls having adventures.