Reality check: you don't need to talk with a lawyer about everything. If you want to find out information about travel in Mexico, you'll almost certainly get better information than 99.99% of practicing attorneys could ever give you by simply contacting the Mexican Consulate. There's one in downtown Boston at 20 Park Plaza. The phone number for their visa and tourism section is (617) 426-4181 ext. 209.
For non-business trips under 30 days, a US citizen doesn't need any visa, but will need either a current passport or other proof of identity and citizenship. I normally spend several weeks a year in Mexico, but it's been a while since my kids were that young. I seem to recall that minor children will need similar documentation and must either be traveling with both parents or have notarizerd statements from the absent parent(s) giving permission for the adults with whom they're traveling to take them into Mexico. Again, all you need to do is call the consulate and ask to get it from the horse's mouth. (i.e., Señor Eduardo).
NB: Not only are all firearms illegal in Mexico without special permits, but even a couple of loose rounds un your trunk can get you a felony conviction in Mexico, which the US Supreme Court has ruled counts as a permanent disqualifier.
Ken