Sara Jahnke received a call from her son’s elementary school that made her heart drop. Jahnke said her 6-year-old, Crosby, had escaped his school last fall and run outside toward a busy street. The Shawnee Mission first grader, who has Down syndrome, needs to be closely monitored because he’s mastered unlocking doors and is known to run off — and when he does, he’s fast. “They gave me a call to let me know it happened and that he was safe. Honestly, he’s a runner. And I think they were doing everything they could. But the class is just so understaffed,” Jahnke said. “He is a high-needs child. And I…