Scientists who study the condition are wrestling with some fundamental questions about the way we define and treat it.

The health secretary has chipped away at the idea that immunizing children against measles and other diseases is a public health good.

© Niki Chan Wylie for The New York Times

Heightened immigration enforcement is stirring anxiety among children whose parents are vulnerable to deportation. “Every day I worry they could take my mom.”

© Jimena Peck for The New York Times

The veto by Mayor Daniella Levine Cava, a Democrat, pushed back on a growing campaign against the mineral, which has been used for decades to prevent cavities.

© Marta Lavandier/Associated Press

New York City is facing a shortage of preschool programs. Real estate developers have discovered that providing day care in their buildings can be good for business.

© Elias Williams for The New York Times

Some things can be seen more clearly in black and white.

The social psychologist Jonathan Haidt discusses the “parents’ revolution” on smartphones that his book “The Anxious Generation” has started.

A new edition of the photographer’s 1988 book is even more relevant today.

Trump says one thing about toxins and does another.