Ana Rosa Villegas López points to the scattered images of her son on the walls of the Mecca Public Library in Southern California. In one, he stares straight at the camera, his sleeplessness etched into the dark circles under his eyes. The walls are covered with photos of children playing on a small square of artificial turf, dust-coated door mats, and the children’s inflamed, rashy arms, runny noses, inhalers, and humidifiers.