Philadelphia District Attorney Larry Krasner is revamping city policies to try to limit the number of children arrested and held in custody. Krasner, a longtime civil rights lawyer, joins a wave of progressive prosecutors trying to address the “school-to-prison” pipeline that emerged in the 1990s. He says that punitive approach did far more harm than good. Philadelphia now holds about 500 juveniles each day in detention centers across the state and beyond. They can cost $200,000 a year or more.