Autonomous cars? Who needs ’em. If you want to improve your city then design it so that children have more autonomy. In this episode we hit the playground with architecture critic Alexandra Lange, the author of “The Design of Childhood.” To grow up into healthy, functional adults, kids need opportunities to experience freedom and independence. Alexandra argues that car-dominated streets make that more difficult. A city designed for cars is a city that’s lousy for families — and pretty much everyone else. Plus: The surprising history of playgrounds.