Millennials moved to cities in droves during the 2000s and 2010s, drawn by the restaurants, the nightlife, and the high-paying jobs. Urban planners and local leaders celebrated, embracing what became known as the “creative class” theory — the idea that attracting educated, creative workers would drive cities’ economic growth.

Real estate developers built accordingly, constructing apartment buildings filled with studios, one-bedrooms, and two-bedrooms designed for singles, roommates, and childless couples. Young professionals could afford the rent, and investors got steady returns. Building larger apartments for families felt risky when the smaller units were working so well. As for single-family homes or townhouses, the types of housing that families with children typically seek out — well, cities weren’t building those either.

Key takeaways:

The strategy worked — until millennials aged out of it. As they now enter their 30s and 40s and start having children, they’re ditching cities where the housing stock never caught up to their changing needs. Across the nation, large urban counties lost roughly 8 percent of their under-5 population between 2020 and 2024, according to data from the Economic Innovation Group. In New York City, families with children under 6 have left at twice the rate of everyone else, a trend that became central to incoming mayor Zohran Mamdani’s winning affordability campaign.

When families leave, cities lose far more than tax revenue; they lose their highest earners, biggest spenders, and the next generation of workers. Because Gen Z is a smaller generation, and the rise of remote work means there’s less pressure for them to live in expensive cities to access high-paying jobs, they aren’t going to fill the gap left by millennial families.

The creative class theory wasn’t wholly wrong, but it missed that cities need to retain those people through their peak earning years, which happen to coincide with when they have children. And as baby boomers retire, working parents become even more critical to a city’s economic strength.

If cities hope to remain economically healthy, they’ll need to build more housing for families with kids.

Why cities haven’t been building for families

Several forces have worked against family-friendly development. Homeowners increasingly tend to be older and past their child-rearing years and often oppose changing zoning laws to allow more housing in their neighborhoods. Worried that the increased density could hurt their property values or quality of life, these more affluent, politically engaged residents tend to wield their outsized influence to keep newcomers out.

As a result, American cities are overwhelmingly zoned for single-family housing, leaving little room for the kinds of duplexes, townhouses, and smaller apartment buildings that offer young families an affordable middle ground between cramped apartments and expensive homes.

There is also resistance to certain kinds of families moving in. “I’m sorry, but class and race matter in America,” said Mildred Warner, a professor of........

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