Basil Al-Reabi was riding home from school in southern Syria, in the fall of 2014, when a roadside bomb struck. The eight-year-old watched as shrapnel shredded his classmates and reduced them to a collection of body parts. As the remnants of the minibus bounced, rolled, and finally came to rest at the foot of a low embankment, three of his limbs were scythed off, his cheeks peppered with shards of blue vehicle paint.