Passport Needed

For those intending trips to Mexico, Canada or the Islands such a Cozumel. A Passport is now necessary to enter AND return.
Makes me wonder how many of our Mexican residents may have gotten stuck in Mexico after the New Year when the law was actuated and they didn't have passports.
I know my neighbors took their 3 children. The wife has a GREEN card & the husband became a US citizen. They go to Mexico to visit family every couple of years and hadn't gone in some time.
I do hope they knew of the law prior to going, but as school begins again tomorrow and they haven't yet returned; it makes me wonder!