I think children's magazines need a good overhaul. The choice is Cbeebies style pre school stuff, cute animals...boys and fashion and heavy messages about looking good and being "sexy" at magazines clearly aimed at pre-teens.
Make up and clothes manufacturers want to sell as much product as possible, so they need to expand their market, so they market at younger and younger girls. They clearly are very interested in making young girls "sexy", because that's what they sell their product on.
The same way tobacco companies are now heavily promting smoking in emerging nations...because they want to sell their stuff and they will sell to anyone who hasn't worked out what crap they are peddling.
Nothing changes unless it is questioned and examined, people used to send small kids down to work in the mines, that was accepted for years and years and took a lot of effort to abolish. It didn't happen because people said "well, if you don't think putting kids in mines is good, don't send your kid down a mine". Similarly, slavery was not abolished by saying "if you don't agree with slavery don't own a slave" becuase there were enough people who saw no issue with it for the traders to still make a nice profit.
Premature sexualisation is about businesses making profits. Sometimes you have to point out that business makes profits from horrible things.