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