Ahoy there, Paul! Welcome aboard planDisney! Ah, starting December off with a
Mexico itinerary out of San Diego? Consider me jealous! My family has cruised on both sides of Mexico, and the Pacific coast of the Baja Peninsula and beyond is gorgeous - you're in for an amazing time!
When it comes to passport requirements for sailings to Mexico, there are only a few that absolutely require passports as your required
Travel Documentation. However, since most Disney Cruise Line vacations that make calls on Mexican ports are round-trip, meaning that your sailing begins and ends at the same port, U.S. citizens can present either an original U.S. Passport, U.S. Passport Card, or Trusted Traveler Card,
OR an original or copy of a state-issued birth certificate AND government-issued photo ID (if over 15 years of age).
Now, while "closed-loop" cruises departing and returning to US ports don't require a passport, I always suggest traveling with one if you can get one! On the slim chance that anything happens which requires you to fly home from a Port of Call, you'll need a passport to do so! You can always check out the latest travel documentation information for more guidance!
Oh, and one additional thing of which to be aware: over the years, various regulations have come and gone requiring minors traveling with only one parent to have explicit consent from the other parent to travel - so there's often confusion on this front.
According to the US Customs and Border Protection website, it is currently advised that minors traveling alone or with only one parent to Mexico have a notarized letter of consent: "Unless the child is accompanied by both parents, the child must have a notarized letter from the other parent or signed by both parents stating, 'I acknowledge that my son/daughter is traveling outside the country with [the name of the adult] with my permission.'"
So if both parents are traveling, it should be smooth sailing! If not, while you may not be asked to produce such a letter by authorities, in the spirit of "better to have it and not need it, than to need it and not have it," I'd suggest you go ahead and have one drafted and notarized just in case!
I hope that helps you check all the boxes as you finish preparing, Paul! Thank you for your question, and if you run into any other rough seas as you continue planning, please drop me another line here at planDisney!
Until then, may your anchor be tight and your compass, true!
Andrew