Sometimes children are so uninhibited that they ask their parents silly questions like, "Why is that man naked?" I am reminded of the emperor's new clothes. You probably wouldn't want to know what the kids are thinking.
Regarding the law, however, I think there is reason not to question what the law is, speaking of the States here. Some people keep saying there is no law against nudity on public land, usually referring to national parks and national forests. By the way, those two different types of places are under different departments and have totally separate missions or objectives and quite probably different mentalities. There are also national seashores, national trails and so on. There are state parks and state forests, too, and most of this applies to them, too. I have no idea what the equivalents are in Europe or the U.K.
Generally speaking, there are national regulations and then there are also local regulations promulgated at park level. They didn't used to even mention public nudity, although the regulations for a couple of places in California did say that public nudity was prohibited beyond a certain point, implying that it was legal up to that point. Naturally, it is only public nudity that is in question.
A few people years ago on another lost forum had mentioned inquiring of a local park director to determine of public nudity, here meaning for something like nude hiking, swimming or sunbathing, was legal. I now don't recall how those may have played out but these days, there is more mention of nudity, along with a host of other forbidden activities, than there used to be. My point is, that if you actually asked an official (and not just a ranger) if nudity were legal, the answer might be "No, but it soon will be."
Another case in point is from the Outer Banks of North Carolina. The family used to own a cottage there and we made a few trips down there every year. Further down the coast from where the cottage was located, was the so-called National Seashore. I liked going down there so as to be able to be nude on the beach. Parking was a problem, though. More recently, signs appeared at the parking lots stating that nudity was illegal. Don't know why but perhaps someone was being indiscreet when the beach patrol came along. I'd have to say that local customs and attitudes trump the law. In some places, including along the Outer Banks, you're lucky to have beach access in the first place.
Incidentally, in the last ten years it has become legal to carry a gun in National Parks--provided local laws are observed--but no nudity!
