Zohran Mamdani will be New York City’s next mayor. The Queens assembly member has rocketed from local political obscurity to national political celebrity in less than a year, making bumper-stickery campaign promises aimed at alleviating the city’s cost-of-living crisis. Fast, free buses. A freeze on rents. Municipal grocery stores. Universal child care.

That last proposal has gotten little attention—perhaps because a relatively small sliver of New Yorkers would directly benefit, perhaps because the proposal hinges on a tax increase Albany would have to approve, perhaps because early-childhood initiatives are so pervasively underemphasized in American life.

When Mayor Bill de Blasio created a universal prekindergarten program and a near-universal 3-K program in New York a decade ago, it was rightly described as a miracle. But in many ways, that undertaking was far simpler than what Mamdani is promising. He aims to provide high-quality, year-round care to toddlers and infants as young as six weeks old, while setting day-care workers’ earnings “at parity” with those of public-school teachers. It’s a cosmically aspirational set of goals, and it faces a steep set of obstacles. But if he can pull it off, the scheme would transform New York’s demography and economy, constituting one of the most radical examples of policy entrepreneurship in recent memory.

I say this as a parent: Day care is great. Good programs enhance children’s cognitive development and school readiness, increasing educational attainment and improving health outcomes decades later. There’s “a mountain of scientific evidence that the early years are the most important,” Philip Fisher, the director of the Stanford Center on Early Childhood, told me.

But unlike other wealthy countries, the United States forces parents to go it alone for the first three years of their children’s lives, and more often the first five. Though targeted investments in kids have among the highest returns of all public expenditures, Washington devotes just 0.4 percent of its budget to young children. Some cities offer municipal child-care programs, and some low-income families get vouchers.