I am looking for the name of a sci fi book I read years ago. It is set in the future. There are flying cars, everything is monitored through a small handheld device. The TV, computer, entering your home, your phone, everything is handled through this handheld device. The company that sells this device originally shipped hundreds of these handheld devices to a third world country and that is how they got popular with the masses.
Young adults are trained as soldiers called angels. They protect the world from invading ships. This ship contains round balls that roll and blow up. The world looks on and helps the angels fight these rolling bombs. An autistic child hears the clicks of the robots, offers his helps and helps the last angel save the world. Unfortunately the angel has to blast off from the invading ship to save herself. She is crippled in the end but alive.