It's not a good thing. Article at The Register (subscription might be required). Excerpt:
The American Psychological Association's report concluded that sexualization was damaging to all women, but particularly to younger girls who are still forming a sense of self. Negative effects include increased risks of depression, eating disorders and low self-esteem. It also discussed the negative impact the sexualization of girls can have on society as a whole as it affects other groups, including men and boys.
One of the biggest catch-phrases that sends me through the roof is, "They have to grow up some time." Sure they do, but at age 11? I hear parents use it all the time to justify everything from allowing kids to go to R-Rated movies to subjecting their kids to a brutal public school environment where sixth graders show up pregnant. Some say, "You don't do them any favors by sheltering them." I disagree. That's precisely what parents do and only a moron doesn't realize it. The parent shelters and then gradually un-shelters: by allowing them to go into the backyard by themselves, then to a neighbors', then to school, then to the movies, etc. Hopefully, by age 18, they're 98% un-sheltered and only need you for financial support and occasional retreats from life's reality. No matter what, you don't throw them into sexually-hostile environments in tight shorts and say, "You're 13 now. Grow up."