It was time for the real estate developer to face facts: No one was really using the common space on the second floor of his new Harlem apartment building.

Rather than let the room remain dormant, the developer, Josef Goodman, had an idea. Why not turn it into something that the neighborhood, rather than just the building’s residents, actually needed: a child care center.

On a recent weekday morning, a dozen toddlers who live nearby passed the deli on the building’s ground floor and climbed a flight of stairs to the revived lounge space, converted last fall into Little Legacy Village Preschool. They gathered on a rainbow mat and wriggled into a downward dog and child’s pose for a yoga session to start off the day.

The preschool is part of an emerging alliance between real estate, one of New York City’s most powerful industries, and child care, one of its most beleaguered.

David and Goliath being on the same team confers mutual benefits.

The city’s child care operators are often desperate for space but strapped for cash. Developers can offer deals on rent or help with converting vacant spaces — all while offering wary neighbors an amenity that, unlike a pet spa or a cold plunge, might actually make their lives easier.