[therealrootuser]

Just trying to understand, what do you mean by a "Mexican US Citizen"?

When I read this originally, I was a bit confused why the child would not have been a US citizen as well by merit of being born to a US Citizen...but I think you're saying that the parent received US citizenship after the child was born?

[throwaway_1928]

Yes, it could be one of many scenarios including the one you mention. It could also be that the child of the US citizen was born in Mexico perhaps during a vacation or prolonged stay.

For that child to become a US citizen would take at least 20 years and perhaps much longer to the point it would not be feasible, like in the case of the author.