Humans are sexual creatures. But I agree with many of my fellow posters who have mentioned the media influence. Sex sells, and so it is sold. I certainly don't agree with it.
I wonder just how much more sexualized children are as compared to the past. Is it that it is more, or that we are seeing it more. Sex is not as taboo a topic as it used to be, and it isn't as shocking for us to see it on TV or the internet. Are we becoming as complacent about our youngsters as we are our media? Perhaps it's like the idea of rape and molestation; it isn't that it's happening more, it's just being reported and talked about more than in the past.
Sexualization is certainly an important issue, what with STDs and the rising population and such. Education is vitally important, and I think that's where the best answer lies. I don't think we should go back to the overly conservative past, but should instead look towards a better educated world. (I still see many teenagers shocked when they hear that pulling out before orgasm is NOT effective birth control!)
As a side note, I wonder if earlier sexualization could also be tied to earlier puberty rates. (This has interestingly been linked to the rise in obesity, since sex hormones are typically lipid-based.)