People are saying he should press charges. I don't really think that's necessary but at the same time he didn't deserved to be assaulted. There's also the argument that she let her kid wander so far away. He looked like he was by himself and looks to be no older than 3 so she's definitely at fault here.
However, the skater has some fault too. He isn't skating at a skate park. I understand it was accident and as someone who has purely skating friends, I know how focused they are and how focused the camera guy can be too, so it's understandable they didn't see the kid.
It should ultimately result in her apologizing and for the skater to be more careful. Unless of course we find out she's a terrible mother who doesn't deserve to be taking care of a child.
Edit: Is it a skate park? If so then yea she's completely at fault.