Universal child care has long been viewed as a pie-in-the-sky item on the progressive policy agenda.

But the idea recently took on new life in some circles, after Zohran Mamdani, the Democratic nominee for mayor of New York City, pledged to make free child care available to every resident in the country’s largest city.

Even proponents of free universal child care acknowledge that the United States is unlikely to establish a national program along these lines anytime soon. Yet Mr. Mamdani’s promise has jolted the conversation about the government’s role in child care and the potential economic impact of a more comprehensive system.

“There are a lot of reasons building a child care system that works for everyone is important to our children, to parents, to employers and to economic growth,” said Julie Kashen, the director for women’s economic justice and a senior fellow at The Century Foundation, a left-leaning think tank.

“Most families need all parents to be working right now in order for them to have any sort of economic security,” she added, “Having access to child care helps with that.”

In a short video explaining his plan, Mr. Mamdani said the lack of universal child care has had a “major cost to our economy.” He nodded to a report from the New York City Economic Development Corporation that found that parents leaving the city or cutting back their work hours because of caregiving responsibilities cost the city $23 billion in 2022.