728.10  Affirmative defense.
  In any prosecution for disseminating or exhibiting obscene material to minors, it is an affirmative defense that the defendant had reasonable cause to believe that the minor involved was eighteen years old or more and the minor exhibited to the defendant a draft card, driver’s license, birth certificate or other official or apparently official document purporting to establish that such minor was eighteen years old or more or was accompanied by a parent or spouse eighteen years of age or more.
[C75, 77, §725.8; C79, 81, §728.10]