There are two children and two sets of parents on every bed. Young mothers cradle limp children. Fathers fuss over immobile babies, barely visible through a maze of tubes and masks. Many more lie on the floor, with parents frantically fanning them to beat the stifling heat. Nurses and doctors run around. Machines blink and glow. High-pitched wailings hush the crowd, sometimes, as little bodies swathed in white are carried out. Or “Wapas jao (go back)” protests ring out as TV anchors or ministers float in and out. But only for a moment. There’s no time to grieve or get angry. The clock is ticking on very sick children.

Time is running out. The shocked nation watches, as heart-wrenching images and stories of suffering from ground zero—Muzaffarpur district in North Bihar—flash across newspapers and television screens. Children are dying like flies every day. A mystery killer is claiming little lives in the blink of an eye: 9 children...