Rebecca Stead chose to set her children’s novel “When You Reach Me”—winner of the 2010 Newbery Medal—in nineteen-seventies New York partly because that’s where she grew up, but also, as she told one interviewer, because she wanted “to show a world of kids with a great deal of autonomy.” Her characters, middle-class middle-school students, routinely walk around the Upper West Side by themselves, a rare freedom in today’s city, despite a significant drop in New York’s crime rate since Stead’s footloose youth.