When children reach 6 years old, their drawings matter. Not because of those purple unicorns or pinstripe dragons but because of how kids sketch themselves and the very real people in their lives.

A collection of drawings by Leonardo da Vinci makes its U.S. debut in Washington, D.C. — not at a museum, but at a public library. The Martin Luther King, Jr. Memorial Library hosts the exhibition.

The door revealed stone steps that led to a room filled with coal. Details from some of the drawings on the walls of the secret room. Despite their age and years covered up, the drawings are “in ...