Everyone, no matter how old we are, is unique - yes? There is no one size fits all answer. Just as I am sure the children you've known benefitted from knowing they were dying, I am confident that this boy benefitted from not knowing.
My husband's 3 grown children did NOT want to know that their father was dying. As a result, when cancer entered his bile ducts, they had only a short few hours to say goodbye and one of them could not make it home in time. As sad as that may seem, not knowing spared them the 3 year long ordeal.
I do not understand it, but some people feel obligated to bring their faith to the dying. Near the end, both my mother and my husband endured this awful experience in hospitals. Luckily, they had made arrangements to come home to hospice care where they were free to walk their own paths. They did not come home to die. They came home to live the rest of their lives.
The boy in this story knew pain, he had endured it for years. Perhaps, you are you talking about the pain of Hell? Are you afraid the boy went to Hell, because he did not accept Jesus Christ as his savior before he died? If so, the fear you are concerned with is yours - not his. Planting your beliefs inside that boy, so late is his young life, would have been cruel.