“Crossing Lines — A Change in the Leading Cause of Death among U.S. Children”
tl;dr: It used to be motor vehicle accidents; it’s now guns. Vehicles, well-regulated, have gotten safer and safer over the years, and there are ever-increasing numbers of guns and related accidents. And those are just the gun-related injuries we know about—there is less data available than there would were it not for the Dickey amendment, which limits federal spending on any form of gun control.