Please can someone help me with this. When I woke up I felt so awful and could remember it vividly for hours.

I turned 30 the day before I had this dream (i.e. I turned 30 on Friday and had the dream on Saturday-Sunday night). I was away on holiday with my wife (also 30, I've known her since we were both 11), and my two kids (5 year old daughter, 23 month old son). Before I went to bed I was rereading The Hobbit and was nearing the part where Bilbo discovered a gap in Smaug the dragon's armour (under his breast). I also flicked for two minutes onto a medieval warrior battle scene on TV, but then watched a comedy compilation show for about twenty minutes before going to bed. I think this probably explains the setting, but I need to understand the core actions.

DREAM START:
The dream started / continued with me and (distantly) my wife in a medieval camp with probably about ten others, when the camp was attacked by goblins that looked like overweight (barrel-like) children aged about six. I managed to escape to a small hole in the woods but one of these goblin children followed me. I was desperate to be rid of him, though he didn't seem too interested in attacking me. I tried to push him away, but he resisted. I found a large kitchen knife and poked him in the chest - his skin appeared too tough to make a dent but he did leave. I decided to leave and try to help my fellow campers, but as I was crawling around the camp with a fondue fork I saw the leader of the attackers (people now, growns too) standing over their infant son. I somehow knew that this was a test or a plea for help, and I was then accompanied by the boy from before to the infant. I knew that I had to kill this child to save my camp, so I stood over him and then plunged the fork into his belly and upward under his ribs. I stabbed for his heart and felt (very disturbingly) something inside his resist the fork and give as I punctured it into his thicker heart tissue. I stabbed him in the heart a few times, each time I could feel the heart resist then give. I was trying to make it as quick as possible, as an act of mercy, knowing that he would be in less pain doing it that way than other ways. I didn't want him to suffer. There was almost no blood and the boy himself only whimpered slightly as I started. No-one stepped into stop me. I was left alone to kill him. I felt awful doing this, but I was then cradling him as he died, crying, rocking him, trying to sooth him as he died, all the time I was saying "I'm sorry James" and "I'm so sorry James" (James is my son's name). I then remember my wife being near me and saying that something "favoured the cruel" (it might have been "heroism" or "bravery", something like that), meaning to make me feel better about what I had just done. Then I woke up.

The boy I killed in my dream was not my son, but I still apologised to him. And I could vividly remember and was haunted by the feeling in my hand of the fork pushing against the boy's heart for days. I tried looking up meanings via dream dictionaries, but I don't think I was killing a part of myself because of the apologies, but I don't know what I feel I have done (knowingly but perhaps reluctantly) to my son. Please can someone help me interpret this. It has really bothered me as I have never had a dream like this.