No, I'm not going to go quoting a bunch of cases. It's fine with me if you don't believe me. There are also laws against disseminating material on bomb making.
Just one search you can do:
Disseminating indecent material to minors. Or Law on same to juveniles.
This is just one state law:
http://www.mass.gov/courts/courtsand...ene-matter.pdf
I'm not going to go look up who has been prosecuted or even charged, but if you search for various topics you'll see plenty of lawyer ads pop up with a list of 'Have you been accused of xyz and need representation."
I'm quite certain you can easily find cases of stores selling material to those under 18 in various states where the sellers were prosecuted.