We’re in a new age of celebrating America’s cities, no longer disparaging and fleeing them as we did through the pre-crash, suburban expansion era.

But who are the cities really for?

Are they for waves of young professionals drawn to glitter and opportunities? Or for America’s seniors, seeking community, supports, activity in their twilight years?

Yes on both counts.

But what about families with pre- and school-age children – especially as schools improve? Are the cities for them too?

That answer, also, needs to be an emphatic “yes.” Because the very future of cities depends on drawing young, child-rearing families.

That theme – the value of truly multigenerational cities – was embraced by a group of liberally oriented city leaders, the “Mayors Innovation Project,” meeting in Washington shortly before Inauguration Day.

Mayor Mark Kleinschmidt of Chapel Hill, N.C., said most people in his university town seem to be 20 or 80 – thus “missing the middle.” That crimps economic opportunity because of a serious lack of investors or workers.

By contrast, Mayor Joseph Curatone of Somerville, Mass., boasted of his Boston-area city, a close neighbor to Cambridge, as “multigenerational,” “the most densely populated city in New England.” Somerville is highly livable, he noted, with a wide range of housing units, lots of little squares and centers, high transit availability and strong civic engagement. Plus, 32 percent of Somerville’s population is aged 25 to 34 – the biggest share of that highly productive age group in Massachusetts.

More typical of today’s America is the Atlanta region, which spent decades developing spread-out suburbs. But the original homeowners are now empty-nesters, reaching senior years and driving less (or not at all). They have needs that profit-oriented subdivision developers never provided. For example: nearby medical and social services, libraries and social centers, people-friendly parks, farmers markets and safe, walkable and bikable environments.

The Atlanta Regional Commission, the mayors’ meeting was told, is trying to popularize the idea of lifelong communities. It even sponsored a “charrette” with 1,500 people discussing ways to encourage new housing options, add sidewalks and make it less perilous for pedestrians to cross fast superhighways. (For details, including links to the charrette led by Andres Duany, click here)

But are these just local issues? Not so, the mayors were told by Mildred Warner of Cornell University. For decades, she said, American communities were designed as if only people with cars mattered. Today’s imperative, she said, is to design our cities, our entire economies, as if every age group matters, including both children and “aging baby boomers who do not wish to be shuffled off to enclaves of only older adults.”

The formula seems a win-win. Both New York City and Charlotte, N.C., for example, have experimented with school buses used in the middle of the day to take seniors shopping. Many communities now encourage seniors to tutor youths, enriching life for both. In Ithaca, N.Y., a Head Start program is permanently housed in a retirement community.

Denser, less car-focused suburbs and towns with multigenerational living can also be encouraged by promoting, on the one hand, three- and four-bedroom houses and apartments for growing families, and on the other, “accessory units” – so-called mother-in-law units in converted garages and other small residences tucked into home lots. Exaggerated fears of rowdy students pouring into such units, or less on-street parking, or imperiled housing values often trigger “NIMBY” opposition. We all too easily champion our American patriotism but deny opportunity to others, from striving families to young learners to returning Iraq and Afghanistan veterans.

And there’s raw economics. Towns make a mistake when they focus heavily on attracting a single group such as young professionals, Warner warned the mayors meeting. Instead, she said, families with young children represent the true “Big Money” – that an average family spends a quarter million dollars raising a child, with three-fourths of that money supporting housing, health care, child care and other needs that create jobs and bolster the local economy.

The sad irony is that the federal government, with its huge defense and growing outlays for Social Security and Medicare, is paying precious little attention to children and families. The idea seems to be these are a state and local responsibility. Locally, some cities, preoccupied with their tax base, even try to zone out families with school-age children.