D.C.’s growth is fueled by 20-somethings. Can the city grow up with them?

During the past decade, Washington has become a magnet for ambitious 20-somethings. Not only does the city offer good jobs and better-than-average public transit, it also boasts food trucks and, of course, cupcake shops.

For a recent college graduate, what’s not to like?

It’s been a remarkable deal for the District, too. The influx of newcomers has transformed the city from a symbol of civic dysfunction and drab government offices to a cosmopolitan hub — an urban playground.

The flood of newcomers did not arrive by accident. City planners and developers have bet big on luring transplants to the region. These are the people who will fill the more than 11,000 new apartments expected to be completed in the area in the next 12 months and whose income, sales and real estate taxes are helping the city’s finances fare far better than those of similar urban areas. Long-blighted storefronts and commercial corridors are being rebuilt.

What D.C. hasn’t yet figured out, or even really planned for, is what happens when this raft of newcomers grows out of one-bedroom condo living. What happens when their lives evolve past the urban-playground stage and they are less interested in speakeasies than in parks for their kids?

Caroline Armijo and her husband joined the wave of new D.C. residents when they moved to the 6th Street Flats apartment building in Chinatown in 2005. At the time, so few people lived there that they had to fight to stop the dumpsters from the Chinese restaurants next door from being emptied in the middle of the night. “A lot of the initial issues were just, ‘Don’t pick up the trash at 4 a.m.,’ ” she said.

A few years later, Armijo, now with her infant daughter in tow, attended one of the first meetings of a Penn Quarter parents group. There she met a mother who made her realize that raising her child downtown would involve more challenges than just finding the right school.

“She kind of scared me,” Armijo said. “She said, ‘The first thing that’s going to sort of push you away from downtown is not the schools — not that the schools aren’t bad — but it is that you realize you need a safe place to play.’ ”

Now that her daughter is 3, Armijo said, finding places to take her is a daily struggle; she swings on bike racks like monkey bars, climbs on a sculpture outside the restaurant Zaytinya or runs atop the National Law Enforcement Officers Memorial. Armijo and other downtown parents have begun crusading for a neighborhood playground, starting a petition and bringing their requests to the D.C. Council, Del. Eleanor Holmes Norton and the National Park Service.

Former D.C. mayor Anthony Williams may not have envisioned the importance of something like a playground in Penn Quarter when his administration began sketching ambitious plans for growth, but the demand is a direct result of those plans. Williams set a goal in 2003 of adding 100,000 residents over the next 10 years and developing at least 15,000 new homes.

He was working off of a Brookings Institution report that said by attracting 50,000 well-off single people and couples without school-age children, the District could increase its revenue by $300 million. Williams and his planners laid the groundwork for nearly all the current major real estate projects and for the new condominiums and apartments that continue to rise — faster than anywhere else in the country since the recession began. If you look up and see a crane today, it is probably at work on a project that Williams’s team set in motion.