Shade's Children by Garth Nix

In a not-so-distant future, the world is ruled by Overlords with the help of their minions, including Myrmidons, Wingers, and Ferrets. All the adults have disappeared and children are forced to live in dormitories, where they are often experimented upon. Once they reach their “Sad Birthday” #14, they are taken to the “Meat Factory” where their bodies are dismembered or harvested to create more of the Overlords’ creatures. A few teens have managed to escape. These teens have developed “Change Talents”, a type of psychic gift that assists in their survival. Ella, Drum, Ninde, and Gold-Eye have been able to stay alive thus far based on the help of Shade, the only “adult” to have survived. He has trained these and other escapees, sending them out on missions to acquire information and supplies. But will being one of Shade’s Children really keep you alive?