Hi there!
I'm new here, but not new to traveling abroad with kids!! #-o LOL
I agree with Roger 100%. It's better to be safe than sorry, so your best bet is to get a NOTORIZED letter stating it's OK with your DH (or the father of your kids) for you to cross the boarder with your sons.
All my (5) kids have passports, but I believe you are still able to cross the Mexican boarder with a CERTIFIED birth certificate, at least for now.
There shouldn