I would like a more specific standard than "nude". Namely the picture should be sexual/pornographic in nature. [0] That is to say, I don't see any problem in, for example, children skinny dipping; nor in taking pictures of them doing so.

Outlawing nude pictures of minors also creates an unnecessary legal grey area with the inevitable exemptions. For instance, I don't think any object to photographing a genital to document a medical issue, so there will be some such pictures that are considered "ok". Outlawing nudity of children in images in general inevitably leads to situtations where one would avoid taking such a picture, or prosecute someone as a result of misunderstanding the context of such a picture.

[0] Legally speaking, this has the obvious problem of defining pornographic. I think the actual standard should be to look for abuse in the creation of the image.