I was raised by European immigrant parents in the Deep South, and I ran around half-dressed all the time 45 years ago, and so did all my "native" friends. Seriously, that whole "Southern modesty" thing when it comes to kids is fairly new, at least when it comes to playwear. Young girls wore really short dresses then, with ruffled panties that were meant to show. Going topless in the summer when playing outdoors was fairly common for little kids a half-century ago, before air-conditioning became common. It was hot as blazes, and it was practical, so no one thought anything of it if we were playing.
Now, skipping the panties IS an issue, I'll grant. Kids do sometimes forget, and with some girls you have to make it point to make sure they remember. I don't have an issue with them just being naked for a minute or two whilst changing clothes quickly, however.
I still have a few summer outfits that I wore when I was not yet in school, and I know that if I dressed DD in them I'd get funny looks. They are what used to be called "sunsuits", little bloomers with an attached pinafore with crossed straps in the back. These days if you see a little girl wearing one she will have a tee on underneath, but we never did. They looked like this, and the top part did not cover anything important; it was just there for looks and to anchor the straps that kept the thing up:
I have a photo of my sister and a cousin playing in the yard wearing outfits similar to this when they were at least 6, and there were boys there playing with them; riding bikes and swinging a baseball bat.
Also, remember the little girl in the Coppertone ad? No top, and that was pretty normal. I saw that swim-bloomers-only look all the time on Florida beaches in the early 1960's. When bikinis became really popular in the late 60's, it mysteriously became necessary for little girls to wear tops, but it really hadn't been before.
I've been known to quickly change my kids' clothing next to a bush in a theme park if they get very wet or very messy, but only while they are still preschoolers. I bow to American sensibilities on that, and besides, once they reach school age they want to do it themselves, and they are just too slow for changing out in the open.