The Fortress of Clouds by J.A.J. Peters
Approx. 94,600 words.
Published on August 17, 2011.
By 2037, Los Angeles has descended into a maw of street violence and child labor factories. High above it all, four children have been raised in a safe and secluded apartment. To protect them from the child-abducting gangs that prowl the streets, their mother has forbid them from ever going outside. Or at least that's what she has told them about why they can never leave.