Not sure if they would just apply for that. They currently only have Mexican Nationality.
I have a son and I have dual citizenship so I registered his birth in Mexico shortly after I had my son since we travel back and forth frequently to visit family but given that his children are older; 2 over 18. I’m not sure if that’s the same process.
One is 13.
The children’s births were never registered in the US.
& well only one is a minor. The other two are considered adults now. Over 18.