Well they make tobacco free shisha so by law it is not illegal to sell to minors. I have researched it, and the law in my state does not cover herbal smoke. So by law, it isn't stated as legal or illegal, so they cannot do anything. I think it's just because they havn't caught on quite yet.
BUT, the sale of herbal cigarettes (Soex for example) could be considered illegal, as sale of any cigarettes
to minors is illegal.