Ari S. knows all about the recent upper- class baby boom. Ari, 39, owns a spacious house in the ritzy New York City suburb of Chappaqua (Bill and Hillary Clinton are neighbors). When he walks through his front door at night, he is, as he puts it, “crushed” by enough children to fill a basketball team’s starting lineup. First he puts the little kids, Phoebe, 5, and Charlie, 3, to bed. Then he helps the older ones, Sam, 12, and Zachary, 10, with their homework. The nine-month-old, John Henry, sticks close to his mother, Susan, who manages the clan.

“I spend a ton of time with kids one through four,” Ari jokes. “When number five can communicate, I’ll talk to him, too.”

Mornings, Ari, who didn’t want to use his full name, takes the commuter train into Manhattan, where he works for a financial-services company that pays him in a year what the average American needs 20 years to earn. In that pinstriped business atmosphere, Ari says, he hears a remarkable amount about children: about having lots of them, and undergoing fertility treatments to have more.

“It sounds sick to say this,” says Ari, who attributes his own brood to his love of family and his Jewish faith. “But there are people who derive status from having many children. It’s become a status symbol.”

Never mind the strain of raising so many little ones. Three kids is the new two, and four is the new three.

Statistics prove that Americans are producing more kids than they used to. Government studies show that from 1984 to 2004, the number of women giving birth to three or more children rose 12 percent, to 18.4 out of every 1,000 women in their childbearing years.

But to explain the Ari demographic, all you need to know is that in the past decade, the rich have gotten much richer. “One thing driving this is the explosion of salary at the top end of the economy,” says Robert H. Frank, a Cornell economist and the author of The Economic Naturalist: In Search of Solutions to Everyday Enigmas. “Certain people are making so much money that it no longer makes sense for their spouses to work, and if one spouse is staying home, why not have a big family?” Especially when a fourth kid is a potent sign of success. Not only does it show that you have the fertility chops to produce a big family and the fiscal chops to support it, but it also says you’re nurturing. It’s an upper-class trifecta.

The rich have always made babies in large numbers. It was only once the baby boom ran its course in industrialized Europe and North America that well-off people started reproducing less. Then the 1990s came along, and a few people started making so much money they didn’t really need two incomes. The issue for them isn’t so much whether they can afford five kids. The issue is what kind of lifestyle they can maintain with five kids: Does each child have his own room in the city and the country? Does the clan take a private jet for Christmas holidays? This kind of one-upmanship is particularly hot in New York. “Among the hedge-fund guys, it’s a joke,” says one Park Avenue woman. “They all have the trophy wife and the apartment and the four kids.”