How to receive a copy of a child's imessages

My child received an iPod touch for his birthday. While he is pretty trustworthy, I do want to be able to keep tabs on what he's texting through iMessage with his friends (some of whom have been known to share inappropriate (in my eyes) information). He knows that I can access his email account at any time and he doesn't have the password to it and is aware that monitoring accounts is part of the deal for him to have an iPod. Is there a way to have his imessages sent to me? I have an iPhone 4S with his email account linked but I want to make sure I have it all set up right. I will also say, I'm having issues getting iMessages from him (he thinks he's cool now that he can text us, lol).

Thanks!