I noticed this too at my school, where most of the kids come from families in or fairly close to the top 1% by gross household income. There weren't many only children among them, and three children seemed to be the most common norm for their families. While the average white woman is managing to produce just 1 or 2 children, these mothers were making at least 3 on a regular basis and were far more likely to hit 4 or 5.
This is just one of the many ways in which you can see the existence of an American aristocracy, an elite core in which the trends plaguing most the population that we complain about don't really have an impact.
Concerned about low fertility? The elite are still having large families.
Concerned about high divorce rates and low marriage rates? The elite
divorce at a lower rate and
marry at a higher rate than everyone else.
Concerned about obesity? The elite don't have anywhere near the average obesity rate, with average BMI's closer to 1970s American or current European levels. Chalk that up to a better (and more expensive) diet and a greater focus on fitness.
Concerned about a lack of employment? The elite are finding jobs no problem, even straight out of school.
Concerned about a lack of money? The elite have recovered just fine from the crisis, even if many of them took big hits when it started.
Class matters. That's just the way of the world, especially in the USA.
For the record, FuturePundit had
an article on this trend six years back and
another in 2009. Interesting to see that its still ongoing.