Much about Orphan-Maker remains unknown. It is unclear whether he is an actual child inhabiting an adult-sized suit of armor, or if he is an adult reduced to an infantile state by Nanny or other means. His mutant powers are also unknown -- his abilities to date all appear to come from his armor or Nanny's weaponry. In Hellions #3-4 and #7, it was indicated that Peter's mutant power is deadly and potentially world-threatening if unleashed, and so his containment suit is required for everyone's safety.
Nannny and the Orphan Maker were exiled to the Pit in Hellions #18 after Peter broke the Krakoan law of "Kill No Man" -- he slaughtered his way through a Right camp and also killed innocent law enforcement that got in his way.