Oberon's Children — Hal Emerson

An orphan girl named Mol wakes in the middle of the night to music. Enchanted, she follows the sound into the forest of Arden, where she is taken captive by a man known only as Oberon; a man who rules a kingdom of monsters. Leaving her life as an urchin far behind, Mol becomes part of Oberon's Bower for reasons she cannot understand, surrounded by hundreds of children just like her that are ruled over by the tyrannical Ilyn. But Mol soon realizes that she was taken for a reason - and that she, and all the other children, have in them the seeds of madness.