True, but in MG, you expect stories featuring those 12 or 13-year-old characters to be read by 8-11 kids. The problem with my story is that it's sitting right there between MG and YA, but it's a lot more MG cause it's got magical creatures and goofy humor. At the same time, I can't do away with describing short skirts and crop tops cause my 12-year-old MC kinda gets whisked off from a middle-eastern society with veils and stuff to a completely secular one. It would actually sound weird if she doesn't bat an eyelash at all the exposed hair and skin, and I totally don't mean it in an objectifying or sexual sense.
I read a ton of MG, especially MG F, and I think you're right that there's a tendency to not describe what kids are wearing, unless it's something unusual (like the robes that Harry had to get at Hogwarts). But there are books that also mention clothes, like the Tiffany Aching books by Terry Pratchett -- they always describe her outfits (her farm dresses, her boots, and her hat) and I loved reading about them.
I think in your case, since your MC is coming from a completely different culture, it would be natural for her to notice the changes in fashion, but she'd also notice this not just in other girls, but in women, men, boys, toddlers, etc. Also, hairstyles, makeup, shoes, the way people behave, and so on and so forth. So to me, the crop tops and short skirts would just be a blip within a sea of cultural change that she has to adjust to.
Cause I can't see how every single girl in every single MG book I've read wouldn't wear these clothes all-year long even in the dead of summer. It seems more like the authors are deliberately avoiding such descriptions. I even remember a scene (forgotten from which book, definitely an upper MG though) where the MC's older sister has a conversation with her from over at a swimming pool and the author never so much as tells us the color of the sister's swimsuit. Do you suppose she's actually swimming with T-shirt and jeans?
The scene you described sounds like a non-issue to me. I would just assume the sister is wearing a swimsuit, unless I'm told otherwise. But also, if the narrative mentions "[SISTER NAME] adjusts her bright green swimsuit before waving at us", I also wouldn't bat an eyelid. It's only if the narrative actually halts to explain in gratuitous detail about her swimsuit that I would find it jarring.
OP, I think it's just that in general there would need to be a reason to describe the clothes, other than simply the fact that they're short or skimpy. Your reason to describe is because short/skimpy is not what your MC is used to seeing. I can't imagine that being a problem - but if it were mine, I'd probably make a note that not everyone is wearing short/skimpy clothes, because frankly not everyone does.
ETA: That's the clothes. I'd steer clear of too much discussion of children's bodies in MG.
Yeah, as with what Mccardey's pointed out, I would find it strange if the short/skimpy clothes are the only things that's being mentioned. What about jeans? Or baggy shirts? Would that not be unusual too?
Heh, as a personal anecdote...I grew up in tropical countries. My family would take vacations to the US or Europe in December, and we'd marvel at how there are people dressed in short sleeves in the middle of winter. I mean, my gawd, my family and I would be shivering in our ridiculously bulky jackets, and here are people in T-shirts, eating ice cream.
There are gonna be different things that stick out to your MC, depending on her personality.