The Supernaturalist by Eoin Colfer

In the future, in a place called Satelite City, fourteen-year-old Cosmo Hill enters the world, unwanted by his parents. He’s sent to the Clarissa Frayne Institute where boys are put to work by the state, testing highly dangerous products. At the end of most days, they are covered with burns, bruises, and sores. Cosmo realizes that if he doesn’t escape, he will die at this so-called orphanage.

When the moment finally comes, Cosmo breaks out with the help of the Supernaturalists, a motley crew of kids who all have the same special ability as Cosmo-they can see supernatural Parasites, creatures that feed on the life force of humans. The Supernaturalists patrol the city at night, hunting the Parasites in hopes of saving what’s left of humanity in Satellite City. Or so they think.