Interesting (for U.S. residents), considering SCOTUS' 2002 opinion in Ashcroft v. Free Speech Coalition, which upheld depictions in cases where actual children were not involved.
http://en.wikipedia.org/wiki/Ashcroft_v._Free_Speech_Coaliti...
http://en.wikipedia.org/wiki/Ashcroft_v._Free_Speech_Coaliti...
This so far has not been challenged, as apparently the guy I mentioned in the Simpsons' case just entered a plea bargain:
http://en.wikipedia.org/wiki/Legal_status_of_cartoon_pornogr...