Fourth World — Kate Thompson

The first book in a trilogy about terrifying genetic experiments.

Danny is different. He's slower than other kids his age, and prone to violent outbursts. But when Danny runs off to find his biological mother, his older stepbrother Christie impulsively follows him. Along the way the two boys are joined by a runaway girl, a bird, and a dog that can speak to humans. However, nothing can prepare them for what they learn when they finally locate Danny's mother at her laboratory, Fourth World. It seems Danny's mother has been performing experiments-secret experiments-with terrifying genetic significance...