The 3-year-old boy had taken only two steps from his mother’s lap when a deafening explosion rang out. The blast caught the woman in the face, blurring her vision. She forced her eyes open and searched for her son around the jetty where they’d been waiting for a ferry, near their small village in south-central Myanmar. Through the smoke, she spotted him. His body lay on the ground, his feet and legs mangled with flesh peeled away, shattered bones exposed. “He was crying and telling me that it hurt so much,” she said. “He didn’t know what just happened.” But...