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					Originally Posted by agzg  The second generation would only be natural-born because the parents were born WITHIN Mexican territory.  So the third generation would be ineligible, because, although the parents were natural-born, they were not born within Mexican territory. | 
	
 @preciousjeni - ^^^ This.
Mexico actually distinguishes between citizenship and nationality in the way that we might distinguish between "franchise" and citizenship.  That is, to be a Mexican citizen you're 18 years old, not a criminal etc.  Their "nationality" is like our "citizenship." 
That said, while it is possible for those null-citizens to be naturalized as Mexican nationals, it's not automatic.  If children brought over to the US as 3 year-olds feel little to no connection to Mexico, why would the third generation feel anything?