I'm with zlurker in that the face is definitely my favorite "part" of a girl.

But I also feel the need to mention something a little more sexual in nature, which is the curve of the lower back of a little girl.

It's been mentioned here before by some people, but for some reason I just find this an incredibly sexy area of a little girl.

The curve itself is hot, but also there's something in the way they stand that contributes to their whole posture. It's like they're puffing out their little sexy bellies, but it's actually just the natural way they stand :) So cute, and it's not as noticeable in boys either.