In the sexualization of younger and younger children, I think that this phenomenon is mostly due to the media and industry targeting the tweenie set as consumers more and more heavily. They've got money to spend, and there's no shortage of unscrupulous businesses selling sex as maturity that want it. What kid doesn't want to appear more "mature" than their schoolmates?
As you said. There's money to be gained on borderline pedophilia, so they make parents dress up their kids like they're little prostitutes.
Not to say there's not a difference between nudity and "challenging" nudity. If it's a hot day and you want your six-year old girl to be topless in the sun, fine by me. If you dress her in a challenging type of clothing, that's a different thing.
As for physically maturing before they're mentally ready, yup, that's a point. Think it's been like that for the last, oh, 200 000 years or so.