There's an odd phenomenon being reported in tony enclaves across the country: highly educated, highly compensated couples popping out four or more children--happily and by choice. In Loudoun County, a suburb of Washington, four-packs of siblings rule the playgrounds. In New York City, real estate agents tell of families buying two or three adjacent apartments to create giant spaces for their giant broods. Oradell, N.J., is home to so many sprawling clans that residents call it Fouradell. In a suburb of Chicago, the sibling boomlet is called the Wheaton Four.
Of course, big families never really disappeared. Immigrants tend to have more kids, as do Mormons, some Catholics and a growing cadre of fundamentalist Christians. But in the U.S. today, the average number of children per mom is about 2, compared with 2.5 in the 1970s. While 34.3% of married women ages 40 to 44 had four or more children in...