At a 1-year-old’s birthday party, Jill Kargman, 32, watched as a mother picked up her daughter from her nanny, posed for a photograph, and promptly passed her back to her caregiver.

Then there are the birthday cards her 3-year-old daughter, Sadie, has received, written in perfect penmanship by 4-year-old friends.
“Sadie can barely draw a face,” Mrs. Kargman said Thursday, sitting in the living room of her Upper East Side co-op.

It was enough to stir up this writer, who put her personal experiences into a new comic novel, “Momzillas” (Broadway Books), which arrives in bookstores today. It is her solo debut after the commercial success of two books she co-wrote about single socialites, “The Right Address” and “Wolves in Chic Clothing.”

What defines momzillas? They are alternately negligent, domineering, competitive, preachy, and as the main character and Mrs. Kargman’s alter ego in the book, Hannah, puts it many times over, “sad.”

Hannah, uprooted from San Francisco when her husband takes a job in New York, deals with a welcoming group of momzillas who try to instruct her on child-rearing. Their lessons include writing first-choice letters to nursery schools, hiring pacifier therapists, and dressing the little ones in Ralph Lauren cashmere sweaters.

The bewildered Hannah slowly finds her moorings while at the same time exposing — with surprising sympathy — what makes momzillas tick.

“These women leave work when they have children, after a lifetime of promotions and accolades. All of that ambition and drive can’t just cease to exist,” Mrs. Kargman said. “They approach motherhood with a vigor of being the best, and in motherhood, there is no best.”

Mrs. Kargman herself is the antithesis of the momzilla, though she has the same pedigree as the most evil character in the book, Bee: raised on the Upper East Side by socially prominent parents, Arie and Coco Kopelman (her father, who helmed Chanel USA, is the chairman of the Winter Antiques Show; her mother is on the board of School of American Ballet), and educated at private schools (Spence, Taft, and Yale).

How does she explain how she defied destiny? “It’s 100% parenting. My parents were loving and cool. We were always normal and we had so much fun together,” Mrs. Kargman said of her parents. “Also, they’d indicate to us the people they felt were spoiled.”

She knew in college she wanted to be a mom. “The girls at Yale were saying, ‘What?’ I was this complete freak. But I was ambitious about wanting to get my personal life in order.”

She met her husband, Harry, when she was 25, and they were married two years later. They have two daughters, Sadie and Ivy, 1.

Her own upbringing is her strongest influence. “I follow my mother’s lead. She is so appreciative of all the moments we share — a simple dinner out or watching Sadie’s face during a movie. You can see her relishing every moment and that has influenced how I live my life more than anything,” Mrs. Kargman said.

As for her dad, “he wasn’t exactly on diaper duty, but he was the most affectionate, doting father on the planet,” she said. “And now — as anyone who knows him can attest — he is an absolutely besotted “Pop” to the grandnuggets.”

Mrs. Kargman wasn’t raised with nannies, and she doesn’t have an army of them. “Even if we could afford 24/7 live-in help, I’d never do it. It’s alone time with the kids I treasure,” she said. Their nanny, Jacky, works 9 a.m. to 5 p.m. on weekdays, which enables Mrs. Kargman to work from home, usually between three and four hours a day.

Mrs. Kargman’s 32-year-old husband, who runs a wireless software company, is involved as much as possible. Although he doesn’t get home until 8 most nights, “when he walks in he totally takes over and is a great bedtime story reader,” Mrs. Kargman said. She keeps her children up until 8:30 so he can tuck them in.

One lesson she took from her upbringing is to use New York as a third parent. “My parents were constantly taking us to shows on and off Broadway. They took us to every single ZIP code,” Mrs. Kargman said.

Mrs. Kargman is following that example, taking Sadie to everything from “Phantom of the Opera” to the Fairway in Red Hook, where they enjoy the view of New York harbor.

Being open to new things keeps her open to getting to know her children. “I don’t miss a class. You learn a lot about your kids in these classes, and I get so much joy watching them in action,” she said.

Sadie takes ballet and a music class. “She is obsessed with ballet,” Mrs. Kargman said. “Music, we sit on the floor, it’s one teacher with a guitar. It’s very mellow, and that’s a good tip: The mellow classes attract mellow moms.”

In the book, the momzillas have their toddlers booked solid. Mrs. Kargman likes the idea of less structure. “If you’re so overprogrammed, you don’t have time to imagine things and you end up more robotic. People who are so psycho controlling of their kids wind up with kids that don’t have a personality. They’re lumps,” she said.

She paused to eat a rice cracker, looking around her living room, with family photos on the mantel and a stuffed frog named Taz on an ottoman near the window.

“It’s all about what you build in the home,” she said. “What I want is to be a mom who, when I look in my child’s eyes, I know that we know each other.”