Eventually once you reach Redcliffe, there will be an option to enter the boy, aside from killing him and confronting the demon inside of the boy. Do not kill the boy. You will not gain much from his death and most likely your allies will disapprove. Instead, choose the option to enter the boy and let the Blood Mage do his ritual. Once you are inside, talk to the father. Once this is done, you must talk to the child "Possessed" and kill the demon inside him multiple times. Once you reach a certain part where you do not talk to the child, but the demon straightforward, try to converse with her. Conversing with her will get you more than just killing her. She will request that in exchange for her life, and the permission to enter the boy's body again in the near future, she will offer you gifts. One is a new specialization. Another is a certain rare item, armor, or weapon. Finally, is pleasure. Pleasure should not be an option, as it does not give you anything in exchange, not even an intimate scene. Select either the item or the specialization. However if you truly do not want to obtain anything useful, kill her. Killing her alone results in the same experience you would get from killing the boy, not to mention the previous times you have also killed her.