It's child porn because...

The nudity doesn't ultimately add anything to the story (hence porn) and the nudity in question is of a child (hence child porn). If the movie was exactly the same but the lead actress was older, no one would make the argument that the nudity added anything, because the reason it's there is the added impact it makes thanks to Brooke Shields being twelve. Seems pretty straightforward to me.

Giving the film the benefit of the doubt, it seems to assume we're going to have a particular reaction to child nudity, something like "oh no, how awful it was for children in that situation back then!" But all the truly unpleasant abuse has to occur off-screen for obvious reasons, so any dramatic impact is toothless. None of the nudity is placed within a context that forces the audience to confront how awful it is, on the contrary it's all supremely tasteful, partly thanks to the whitewashed characterisation of the most artificially appealing pedophile in cinema history, Bellocq. And by using real child nudity in an attempt to demonstrate how exploitative of children people were back then, the film ignores Its own message.

It doesn't help that there's effectively no story. There's almost no focus on what Violet is actually feeling at all, instead there's an alternation between scenes where she acts like a child and scenes where she earns her keep as a prostitute. I got the impression I was supposed to sympathise with the character soley because she was a child in a sh!tty situation, not because the writers gave her interesting traits, or at the very least, conveyed an impression of how she saw the world.

We could argue how to define porn, of course, but I don't think that's difficult: it's where the nudity is the point. If this movie hadn't had Brooke Shields naked no one would even remember it, as there's little dramatic content and no plot. The main character has, from beginning to end, no ultimate control over her fate - and regardless of how realistic that is it still makes for a lousy story. If they had made the narrative more character-based, so it hinged on something that Violet could have some influence over, perhaps a story about a child prostitute in this era could have worked... but not like this.

1/10, one of the most pathetically misguided exploitation flicks ever.