I would think he should not have gone to jail at all IF he had done ONE wrestling move and the little girl died. That scenario would go something like this:
L: Let me show you a wrestling move!
T: OK!
L does the move, the little girl hits her head, etc., and dies. L is shocked, appalled, etc.
Such a situation would be an obvious, if tragic, accident and no child should be imprisoned for something like that.
But, the fact that he repeatedly did moves to her - after he cracked her ribs, did she not cry out in pain? Could he not see she was injured? After he hit her head, if she was still alive, would she not have been crying?
The fact that he did SEVERAL moves on her and caused MULTIPLE injuries implies that there was something not right.
I had a kid brother. I was 5 years younger. Even when I was 8 years old, I knew that, given how much larger I was then him, I should not really hit him. How could a 130 pound boy not realize he should not hit a 50 pound girl? Again, something just seems not right here. I could see him trying ONE wrestling move in a restrained manner (not going all out) but for him to repeatedly and strongly do moves... no, something is not right.