I've been reading up on this phenomenon, which is slowly coming to be known as the Lolita Effect. The idea is that the media plays a large role in the fact that young girls, and boys, are growing up so fast. Heightened levels of sexual activity on TV, games, etc, not to mention the growing acceptance that being thin is the only way to be pretty and other such crazy things is what has been pinpointed as the reasons why this is occuring. I have to personally agree.
Take, for instance, the simple matter of Barbie and Bratz dolls. Barbie is able to do anything, but you only see her the same way. Blonde, blue-eyed, and with body measurements that would cause her to be unable to walk. Then we look at her competitor, the Bratz dolls. Of equally unrealistic measurements, these dolls serve no purpose except to teach young girls how to be "sexy". Just walk into the toy aisle at the store and you'll see exactly what I'm talking about.
While part of this is from the media, it also is from parents not taking responsibility. Sadly enough, sex talks need to come at a much younger age, but parents fail to see the differences between their era and the one which is approaching.
You might find this article interesting. I know I did. Just a warning, some sexual terms are within, so it is slightly sensitive material. Nothing inappropriate, just different, very common situations society is seeing now.
Grade-school Lolita: ‘So Sexy So Soon’ - Back to School - Today.msnbc.com