Andrea Peyser: Nuclear (family) alarm! Georgina and her father Michael Bloomberg attend a gala event at The Waldorf-Astoria in 2010.

Nuclear (family) alarm!

Georgina Bloomberg is the face of the millennials — a generation of young adults unfazed by the old rules of morality.

At age 31, the elder of billionaire former Mayor Mike Bloomberg’s two daughters is a professional equestrienne who, in December, gave birth to a son, Jasper Michael Brown Quintana, by her horseback- riding beau, the Argentine-born Ramiro Quintana, 37. And if you thought the arrival of a bouncing bundle of joy might propel the heiress to gallop to the nearest chuppah, you’d be mistaken.

“I honestly don’t know if I’ll ever get married,’’ Georgina Bloomberg told Hamptons magazine. “It’s just something I never really cared about, but I’m not saying I never will.’’

Such ambivalence. With that, Georgina Bloomberg has gone from a lady who might once have been considered a rebel or worse, a fallen woman, and transformed into something quite different: A normal, average American.

Go back to 1960, the “Mad Men’’ era when wives stayed home to procreate, and the proportion of children born to American women who were not married stood at a mere 5 percent.

Over the decades, the number has risen in a dizzying fashion. Last year, as has been the case for the previous five years, 41 percent of women give birth without the benefit of marriage, according to data collected by the National Center of Health Statistics. Despite the post-baby union of such couples as reality TV creature Kim Kardashian and rapper Kanye West, more than four in ten women with children either chose not to get married, or don’t consider wedded bliss, or misery, an option.

But what happens to the kids?

As numerous studies have shown, children who grow up in fatherless households are more likely than those in standard, two-parent homes to grow up poor, drop out of school or get in trouble with the law. Or, in the case of girls, to get pregnant as teens.

“After birth, children whose fathers play with them, read to them, take them on outings, and care for them have fewer behavioral problems during their early school years. And they have a lower risk of delinquency or criminal behavior as adolescents,’’ Paul Raeburn, author of “Do Fathers Matter? What Science is Telling Us about the Parent We’ve Overlooked,’’ wrote in a piece published in this newspaper.

But should we worry about Georgina Bloomberg? While we moan about the plight of children raised by unmarried moms, or ones whose dads are mere visitors, the biggest problems associated with kids from broken homes or ones in which the parents were never united legally, exist mainly among the 99 percent — not the stinking rich.

Don’t they?

This month, Kevin McEnroe, the 28-year-old son of former tennis great John McEnroe and actress Tatum O’Neal, was busted in Manhattan while allegedly trying to score cocaine and prescription drugs from a drug dealer. Young McEnroe not only came from a broken home, his mother lost custody of him and his two siblings in 1995 due to her heroin addiction. The wealthy are not immune to the ravages of parental dysfunction.

And it’s only getting worse.

Millennials — defined as people who became young adults around the year 2000 — are on track to have the lowest rates of marriage of any previous generation. More than 30 percent of millennial women are expected to remain single by age 40, according to an Urban Institute report. And while the percentage of babies born to black, single women has been pegged as high as 71 percent by National Vital Statistics Reports, the racial gap has narrowed since 1980, with 29 percent of children born to white women without the benefit of marriage.