I've tried to read most of the posts here. What I am taking in is the following:
Sally Mann photographed her own children growing up, evolving into teengers as all children do. She had their permission at the time, and perhaps even more importantly she has the permission of them as near middle aged adults to publish and exhibit those photos. The subjects of the photos are now plenty old enough to be involved in those decisions themselves.
The images I've seen don't show anything I could reasonably interpret as pornography. There are some poses that might be described as precocious but no sexual acts, nothing designed to titillate or elicit sexual arousal in the viewer. Frankly if that's what you see, then we are poles apart and I encourage you to clutch at those pearls a little less tightly.
I am reminded of a case in the 80s or possibly early 90s here in the UK when an emplooyee at Boods (think Walgreen's) reported a customer (who I recall was a celebrity) who had given a film to her local Boots for D&P. On it were photos of her young children naked in the bath, in the garden and so on. The over-zealous employee thought these were illegal and contacted the police. It made national headlines, but the eventual conclusion was that these were simply family photos with naked kids. The police and Boots confirmed that simply being naked, for kids and adults, was not a problem with photos.
I don't see any parallels to street photography where you are generally photographing people you do not know. Additionally, people are generally not naked in the streets except for things like the naked bike ride, when they know they're going to be photographed.
There have been issues on beaches, where once people waved cameras about everywhere there is sometimes now concern that anyone with a "big lens" is up to no good and photographing kiddies naked or in swimming clothes. Again though, the concern would be that if there were any nefarious persons doing so....they'd be photographing children of people they do not know, and would therefore not be simply documenting their or a friend's family at the beach.