As people get more educated, they realize their standard of living--and that of their kids--is higher when there are fewer mouths to feed. The days of more kids being an advantage-- to help around the farm--are to a large extent over.

And believe it or not, they recognize the correlation between standard of living and size of family in Mexico too--as people join the middle class, size of family drops. The Mexican government even sponsored a campaign to that effect, to encourage the process. Yes, I know the Catholic church is a countervailing influence.

But in the US, that has been the experience for many immigrant groups. There is no reason to think the 2nd or 3rd generation Mexican-Americans would also not have smaller families. We've had the "yellow peril", now it's the "brown peril". Same tired quasi-racist or baldly racist arguments.