In the 37 days following a mass shooting at their school in Parkland, Florida, the teenagers from Marjory Stoneman Douglas High School organized a worldwide protest against gun violence and then moved from that straight into a nationwide bus tour to encourage people to vote against politicians that were in the pocket of the gun lobby. We’ve seen these young people in the eye of the media, but director Kim A. Snyder’s new documentary Us Kids goes behind the scenes to show the toll taken on kids who were traumatized but felt it was their duty to fight …