Thirty years ago in New York, families were made in fours. Almost all of my friends from grade school and high school had one brother or one sister. Being an only child signaled financial or marital problems, and having two siblings – well, that usually meant one of three things: The parents hadn’t mastered the fine art of birth control; following a divorce and remarriage, step-siblings and half-siblings were joining the family; after two boys, or two girls, a rather adventurous family was hoping for a third of the opposite sex.

But today, in Manhattan at least, three is the new two. At my son’s nursery school on the Upper East Side, there are as many families of five as there are of four. And these families seem to understand birth control, have (so far) side-stepped divorce, and appear genuinely thrilled at the thought of adding either a boy or girl to the mix.

Big families are in vogue, and apparently the only thing hipper than toting the latest Tod handbag is toting a newborn baby on the other arm.

Of course, this trend is not reflected by the U.S. Census Bureau, which shows that in every state except Utah and Idaho, the average number of children per family is less than two. But this city often beats to its own drummer.

Maybe it all began with Madonna, who gave birth to Lourdes eight years ago, and more recently gave birth to Rocky. She flaunted her belly and brought the sexy back to mama.

Since then, Hollywood has turned motherhood into the latest trend, with Kate Hudson, Gwyneth Paltrow, Reese Witherspoon, Catherine Zeta-Jones, and Courtney Cox Arquette all following suit.

Designer maternity clothes by Liz Lange, Diane Von Furstenburg, Seven Jeans, and Elie Tahari almost make gaining 30 pounds an appealing adventure to some fashionistas and Hollywood starlets.

And of course, having a third child often dictates the purchase of a new vehicle, perhaps in the form of the uber-trendy SUV. Despite the fact that study after study has confirmed that SUV’s are less safe than regular cars, safety-conscious moms and dads are still lining up to buy the Durangos and Explorers. For those of us who really want to be fully fortified, a Range Rover, Land Cruiser, Suburban, or Denali is the automobile of choice.

Years ago having the latest BMW was the ultimate status symbol, but today it is having a third and – gasp – fourth child to fill the stylish X5.

But making the move from one-on-one to zone defense surely requires more inspiration than People magazine or the latest catalogue of A Pea in the Pod.

In almost all the families of six that I know, and the majority of families of five, the mothers do not work outside the home. Maybe this generation of women feels liberated from the previous generations of feminists, to whom being a full-time mother often translated to being “just a mother.”

“My kids will be my finest contribution to making this world a better place,” said a mother of four that I know. “And even with four of them, the number of years that I will be really at home doing heavy-duty, handson care, is surprisingly small.”

Maybe in this post-feminist age women have figured out that for some of us, raising our children full-time is the most fun and fulfilling job around, and that even if our society doesn’t recognize its value, we can see the rewards in our children’s faces every day.

Or maybe it’s the increased wealth of Manhattanites that is driving up the number of children per family. Many private schools in Manhattan have raised tuition fees to more than $25,000 a year. Fifteen years of $25,000 times three adds up. And who knows how much college tuition will be 10 or 20 years from now.

And for some, having a third child requires an additional set of hands in the household. Whether one parent decides to work less or not at all, or the family decides to hire additional help, solving this problem can be emotionally charged, as well as expensive – and more families are able to afford the help.

Of course, it may simply be that New Yorkers have finally discovered what our great-grandparents knew so well: That having children is the greatest blessing of all, and that the more you have, the more you are blessed. If a new wardrobe and new car comes with the package – hey, those things never hurt.

Readers can address their parenting questions to Ms. Berman at sberman@nysun.com.