Awww, so sad with the little guy.
I'm afraid I'm going to have to side with Riven on this as well. I think you are prolonging this to no good end. He looks as though he was crushed. With the little guy having poop on him, only being able to squirm, not even move, as Megan said, it's a quality of life issue. He should be up running around with his siblings, not laying on his side while they run over him. This isn't a little injury that is going to improve, I'm afraid.
I know how hard this is for you, believe me. I've been there more times than I want to count, but I also know how much harder I fought when I first started breeding, because I thought every single kit should live. It just doesn't always work that way. Sometimes, they truly aren't meant to.