I can't find anything of the web under USPS laws, but I think Zach being a minor means that his parents have the right to intercept his mail and control his other contacts. I think that LIA must return to sender or forward to parents to stay within the law. If they just destroy them they could be in trouble as you said.
And, if you didn't put a return address--they can't return to sender.... :c) Yeah, the parents need to see how much Zach is loved for who he is. *sigh* If only they could do the same.