This is really interesting, this topic.
Because I also flinch occasionally when I see what teen (girls, always girls) are wearing, and I have to wonder to myself why it is.
Having given it some thought, for me, I think it goes:
Some adult women are very sexually attractive to men. Some adult women like to be sexually attractive to men in a general way, for whatever reasons they have. (Many women don't , they want to be found sexually attractive by people they also find attractive and not the rest of them thanks actually you can stop following me now). Anyway, the women who are very sexually attractive to men have certain attributes that probably haven't changed over the millenia - things around symmetry of face and curviness of hip and slenderness of waist and so forth. And thus fashions over the years will look to accentuate these points on women generally, whether they are actually in the realm of very sexually attractive or not, and depending on the prevailing mores of society (ankles / breasts / hair covered / uncovered and so forth).
Of course many women and girls who are very sexually attractive don't like the attention and so try to hide their body and looks - which is very difficult and life for them can be very difficult indeed.
So then we are left with the fashion for women who are adults and if they want to of dressing in a certain way which is understood by society to mean "I am trying to look sexually attractive" and this of course changes over the years as to what it consists of.
But girls will always emulate women - that's just normal and standard - and this is where the problem comes as (as a poster previous has pointed out) the girls are dressing this way because it is the fashion. They are not (almost always not) dressing that way because they even want to look attractive to boys their own age, and you will be hard pressed to find any who dress that way because they want to look sexually appealing to a random passing 60yo lech.
So, really, the problem is getting the intent of some adult women and assuming that intent is there in much younger teens and even children.
Then, also, well it's not the clothes, is it. If you take "sexy woman" clothes and makeup and put them on a man, or a boy, people don't make comments about them being promiscuous. If you put them on a 4 year old, people think that's a bit weird, but they don't think the 4yo is "slutty". It's only when you put the clothes on a female aged about 8 up that people start making all these unpleasant comments. And, as we all know, even if girls and women don't wear these clothes, they still get the kind of treatment from men that presumably is being invited by "the clothes". it's not though is it, it's the young female person in the clothes and it doesn't matter what they wear it'll still be that way.
So in short, saying that girls in X clothing are is very basic fundamental victim blaming. Before anything has even happened they are saying it is the girls fault for choosing to wear certain clothes. Which is patently ridiculous.
And of course anyone who thinks that adult men are liable to assault female children just because they've got a certain type of shoe on is deluded. Paedophiles don't select victims based on their shoes.
It's just all pre-empting the usual victim blaming shite.