The U.N. children’s agency said Thursday that violence in Myanmar’s western state of Rakhine is driving as many as 12,000 children across the border into Bangladesh each week, warning that hundreds of thousands are at risk of waterborne disease in overcrowded and unsanitary displacement camps. Eight weeks into a calamitous crisis on the border between Myanmar and Bangladesh, tired and desperate Rohingya Muslims, young and old, continue their exodus to what is becoming the world’s largest refugee camp.