These were not exceptional cases. I wasn’t even probing for them. But mother after mother described some version of the same dynamic — a struggling older child steadied, sometimes dramatically, by the responsibility and tenderness of caring for a younger one. Today’s middle-school- and high-school-age children rarely have that experience. They do not share a home with an infant or an adoring toddler. Many will not even remember a time when they did.

The most striking story I heard came from a West Coast mother of nine. Her seventh child was born with a chromosomal abnormality so rare that she could find no other case to match his profile. For months, this mother told me, she lived at the hospital while her older children, without being asked, stepped up to cook, do the laundry and care for one another while their father went to work. When the baby finally came home, his siblings accompanied him to every appointment — cardiology, X-rays, therapy — learning to help with gastrostomy-tube feedings, working like nurses. Specialists were impressed by his progress and speculated that the kids were behind it. Whatever the therapist assigned as homework, the mother posted for her family to see. If the baby needed to be flipped to build upper-body strength, whoever passed by would flip him. Morning and night. Without anyone setting out to teach them, these children had become habituated to caring for one another.

We hear constantly that Americans are more atomized, more polarized, more isolated than ever. Some say it’s the screens. Some say social media. Pundits on the left and right blame our political order and the ideas that animate it. The common diagnosis is that our system can no longer cultivate the virtues needed to sustain it: Virtue has been a casualty of freedom. The mothers I interviewed pointed to a different explanation. The problem isn’t freedom. It’s that we have lost the primary institution where virtues are formed — the household in which children form one another.

The 19th-century American writer and preacher Orestes Brownson once described his upbringing in just these terms. “Properly speaking I had no childhood,” he wrote, adding, “Brought up with old people, and debarred from all the sports, plays and amusements of children, I had the manners, the tone and tastes of an old man before I was a boy.” A sad misfortune, he called it — “for children form one another, and should always be suffered to be children as long as possible. Both children and youth are quite too short with us, and the morals and manners of the country suffer from it.”

Where does this leave us? There are no easy answers. Smaller families aren’t just about choosing to invest more in each child. They also reflect difficult trade-offs that fall heavily on women: career pauses that compound into lower lifetime earnings, and promotions missed during the caregiving years. And many never reach this calculation at all — suitable partners are hard to find, fewer young adults have practical experience with the joys of children (itself a consequence of the smaller families that came before), and life’s uncertainties make long-term commitments feel premature.