The rolling backpack was grey with bright orange zippers. Made by Totto, a popular South American brand, the backpack had been 13-year-old Cristian Rubio’s hand luggage on his flight from Ecuador to the United States a week earlier. It was one of the few things of personal significance that he’d brought with him. “I had some crazy memories with it, like friends hopping on my backpack and racing each other,” said Rubio, now 18. He was glad he had something from home as he walked alone into North Middle School to start eighth grade in his new hometown of Sioux City, Iowa. Certainly, nothing else about his life was normal that November day. He and his older brother, Esteban, were staying with their grandmother, who had traveled to the states with them. The Rubios had decided to move...