Since I used to be in the industry, I always purchase travel insurance. Not just in case I get sick and can not go on the trip but also if I get sick or injured on the trip out of the country.
I carry my Passport even on the 3 or 4 night Baja cruise where a birth certificate will work.
I have had travel insurance pay out a few times, one time dad got the flu so the family could not go, a doctors note faxed in to the insurance company and all was paid out. Very good service from the travel insurance sold through Vacationstogo.com, no problem filing a claim, polite service and quick pay out.
We have been lucky to date and have only used it for illnesses before the trip. None of us have ever gotten ill or injured on the trip.
When you get travel insurance be sure to get enough so it also covers your flight and hotel cost, not just your cruise. Take a copy of the policy with you, you may need it on the ship or if in port. Some policies also have death benefits just in case. Ask what the policy does cover and keep receipts for hotel, car rental and flights that will be needed if you file a claim.
My thoughts go out to the family, what a terrible thing to be ill in Mexico, not be able to talk to the doctors and have not insurance or money to pay for emergency surgery for your child.
Respect to Carnival Cruise limes for stepping up and not just dumping the family in Mexico with a sick child. I'm happy to hear they helped with interpreters in Mexico, getting passports for the family and with raising funds for the family to pay the hospital bill. Good job Carnival.