Welcome to “TriBurBia.”

That’s what the former artists enclave known as TriBeCa is now called by the young families rapidly putting down roots in the neighborhood.

Baby buggies crowd recently lonely sidewalks, nursery schools are fielding a record number of applications, and a slew of new businesses catering to the under-5 set are capitalizing on TriBeCa’s transformation into family-land.

Less than five years ago, after the attacks of September 11, 2001, the Triangle Below Canal just north of the World Trade Center was uninhabitable. Lower Manhattan’s future looked so bleak that a state agency gave away $500 a month for up to two years to people willing to move downtown.

These days, $500 won’t put a dent in the rent. The neighborhood now boasts the city’s priciest apartments and is establishing itself as New York’s most family-friendly neighborhood amid the proliferation of converted residential lofts.

“Our secret is out,” a 39-year-old TriBeCa resident, Karie Parker Davidson, said. “There used to be nobody on the sidewalks, and you knew absolutely everyone in the neighborhood. Now, there are tons of strollers, but chances are you still know everyone.” Ms. Parker Davidson, an attorney who moved with her husband to the neighborhood in 1991, has two daughters, ages 4 and 6.

“It’s starting to feel a little crowded,” Ms. Parker Davidson said. “The economics are different; the demographics are different. People here have tried to maintain that downtown, artsy feel, but you can’t have an edgy, artistic neighborhood without artists.”

Still, it is the enclave’s perceived intimacy and the stellar reputation of Public School 234 that convinced a father of 5- and 2-year-old boys, Daniel Gluck, to head downtown.

“You go into a store, and say, ‘Hi Bill’ or ‘Hi Mary,'” Mr.Gluck, 38, the founder of the Museum of Sex, said. “It’s not that it feels just like the suburbs, but there is a sense of community that you don’t get on the Upper East Side, or even the Upper West Side.”

U.S. Census data from 2000 shows fewer than 35,000 Manhattan residents lived below Canal Street. While toxic fumes and debris forced some area residents from their homes for weeks and months after September 11, Lower Manhattan’s population has since soared past 50,000, according to the chairwoman of the area’s Community Board 8, Julie Menin.

The influx of families is breeding a new generation of schools and family friendly businesses, and many more are anticipated as six new luxury condominiums open in the next few years.

A 23-year TriBeCa resident who is a local history columnist, Oliver Allen, said he never would have predicted TriBeCa’s fashionable popularity and abundant wealth. Mr. Allen writes about neighborhood history for the Tribeca Trib and is the author of the 1999 book “Tales of Old Tribeca: An illustrated history of New York’sTriangle Below Canal Street.”

“When we moved to the area, we thought it would always be a little unusual, a little peculiar, not upscale in any way,” he said. “Boy were we fooled.”

A ranking from Forbes magazine shows median home sales topping $1.8 million and $1.6 million in TriBeCa’s 10013 and 10007 zip codes. The high prices aren’t an impediment to young families enjoying inheritances, Wall Street salaries, and real estate riches.

“Even with all the money that’s coming down here, the people have made a conscious choice to get away from some of the stuff going on uptown – the social ambitiousness,” an Upper East Side native who moved to TriBeCa in November 2001, Catherine Greenman, said. “They want a tighter sense of community. It is in danger of getting more crowded but, hopefully, that feeling and that intention will remain.”

While social ambitions may dissipate south of Canal Street, preschool competition only heats up in a neighborhood with few options. Ms. Greenman, a 39-year-old writer and mother of two sons, ages 4 and 2, said she was asked to write three recommendations for would-be students of TriBeCa preschools.

Neighborhood growth has forced P.S. 234, which is now building an annex, to operate at more than 120% capacity, closing a computer lab to accommodate the overflow and shutting its prekindergarten program.

The increasingly competitive atmosphere for preschool is a relatively new phenomenon in the neighborhood, the founder and head of Washington Market School, Ronnie Moskowitz, said.

“It became more of a concerted effort about five years ago,” Ms. Moskowitz said, reflecting on the 30 years since she opened a school in her TriBeCa loft. Washington Market now serves more than 300 students in two neighborhood locations.

With the classes full at the neighborhood’s existing preschools, the Montessori School of Manhattan opened three years ago with 22 students. This fall, the Beach Street nursery school will reach its cap of 250 students. It is turning away 90% of applicants, the head of school, Bridie Gauthier, said.

“I don’t see it dying down anytime soon,” she said, predicting that the neighborhood’s population would continue to grow for at least another 15 years. To meet that demand, Ms. Gauthier said the school – where annual tuition ranges from $10,000 to $20,000 – plans a second Lower Manhattan location in September 2007.

For older children, the for-profit Claremont Preparatory School opened on Broad Street last year. Enrollment at the school is expected to double to 120 students next fall, the incoming headmaster, Irwin Shlachter, said.

Another yardstick of TriBeCa’s baby boom is the influx of young family-friendly businesses. An indoor activities center for young children and their parents, “miniMasters,” opened in April with classes including motherbaby Pilates, art, ballet, and Suzuki-method violin and piano lessons. Parents can get manicures, pedicures, and massages while their children play.

“It’s a wonderful place to hang out with other mothers,” a TriBeCa resident with a 2-year-old daughter, Stacy Cadolini, said. “It’s a great networking environment.”

Ms. Cadolini said an indoor play space is a delightful departure from the crowded Washington Market Park along the West Side Highway. “It’s so busy all the time,” she said. “You can’t go there during certain hours because it’s so crowded.”

The neighborhood’s demographic shift also means earlier crowds at Roc, the Duane Street Italian restaurant that Ms. Cadolini and her husband, Rocco, own. “At first everyone was single, and now it seems they’ve all gotten married and had children,” she said.

Families are the core clientele of the Soda Shop, an old-fashioned milkshake and sandwich shop that opened last fall on Chambers Street. “The number of pregnant women you see – it’s unbelievable,” an owner of the Soda Shop, Craig Bero, said. “It’s a real community down here.”

Mr. Bero said he hopes the Soda Shop will be a first-date place for TriBeCa’s youngsters when they hit their teens. For now, he’s creating a tree house-themed room for children’s birthday parties that will include a cupcake bar, a pinball machine, and a bevy of vintage toys.

“Living here – it’s almost as if you bought a house in a new, family-friendly development in the suburbs,” the owner of TriBeCa Girls clothing store, Bryn Asen, said. “There are not a lot of single people, and there aren’t many older people.” Ms. Asen and her husband, Robert, opened the store ago on Duane Street to serve the proliferation of young “TriBurBans.”

While it’s a sure boon for business, the rapid growth is met with ambivalence among old-timers who want to preserve TriBeCa as a lightly populated haven. The neighborhood’s crowded Food Emporium grocery store will soon compete with a Whole Foods market slated to open alongside a Barnes & Noble bookstore at the base of a 420-unit condominium complex on Warren Street.

A TriBeCa resident since 2000, Isabel Rose, said the neighborhood “is heaven if you have kids.”

“There’s a total absence, right now, of pretension, of showiness, of gaudiness that’s associated with uptown living,” Ms. Rose, who is in her late 30s and has a 4-year-old daughter, said. “Outside the preschools here, you don’t have the pileup of Town Cars that you might see in front of the 92nd Street Y.”

She said she hopes the neighborhood can strike a balance between development and preservation. “I’m hoping we won’t end up with three more Starbucks and a Victoria’s Secret – the shops that have turned the Upper West Side into a mall,” said Ms. Rose, author of the 2005 novel, “The J.A.P. Chronicles.” “I hope that TriBeCa gets the amenities it needs while maintaining its individualistic spirit. I do hope it’s not spoiled.”