Heartbreaking drawings by children held inside a notorious immigrant detention facility lay bare the misery behind its walls—as guards stand accused of seizing their artwork to silence them. The sketches, obtained by ProPublica after they were smuggled out of the South Texas Family Residential Center in Dilley, Texas, include a pencil drawing of a wobbly bus carrying stick figures, below which a child has written in Spanish: “Me quiero ir”—“I want to leave.” Dilley holds roughly 1,400 people behind a metal fence in a cluster of trailers and dormitory buildings 80 miles southwest of San Antonio. The facility has been...