Mexican citizens moving to Mexico do not need a passport. Some evidence of citizenship will be helpful, however.
Foreign citizens (such as those from the U.S.) need to secure permission from the Instituto Nacional de Migración, which will ask you to prove your identity and your nationality before issuing you an FM3 or FM2. The passport does both; alternatively, INM might accept your driver's license (identity) and your birth certificate (nationality) if dulytranslated into Spanish. Details at
the related link or at the Mexican consulate or embassy nearest you.
I would make sure I had a US passport,
Yes, you need a valid passport for a flight to Mexico.
Yes, babies need a passport to travel to Mexico.
Yes, children need a passport to travel to Mexico.
Yes, infants need a passport to travel to Mexico.
Yes, children need a passport to fly to Mexico.
Yes, children need a passport to travel to Mexico.
Yes, minors need a passport to fly to Mexico.
Yes, minors need a passport to travel to Mexico.
Yes, you need a Mexican passport to travel to Mexico.
Yes, you do not need a passport to fly within Mexico if you are a Mexican citizen. However, if you are a foreigner, you will need a valid passport to travel within Mexico.
Yes, you need a valid passport to travel to Mazatlan, Mexico.