There has been a stunning decline in the fertility rate in Mexico, which means that, in a few years, there will not be nearly as many teenagers in Mexico looking for work in the United States or anywhere else…
Another reason for the particularly sharp decline in Mexico is the cultural influence of the United States. Some politicians fear that we are being "Mexicanized." In fact the opposite may be underway. NAFTA, our mass media, the more widespread use of English, and the large number of people going back and forth (legally or otherwise) mean that Mexicans are increasingly influenced by our culture, and that implies fewer babies.
I'm not sure this particular trend is attributable to Americanization; plunging fertility rates are a global phenomenon, and it's not as if they're falling fastest in countries most enamored of American culture. (Iran's fertility rate dropped 64 percent between 1986 and 2000.) Mexican-Americans, incidentally, have a higher fertility rate than Mexicans.
Via Will Wilkinson.