you can tell the parents are negligent just by reading what they are quoted as saying about their kid also by reading their names
The real telling thing about the parents is they allowed him to be photographed like he is some kind of prizefighter. If they really want to deny these claims and say that their kid isn't some useless sociopath that is running around punching and kicking everything in sight, how about providing a picture where he is sitting down in a chair and coloring between the lines?
As for the injuries, who really knows. It doesn't really take a lot of force to cause injuries to the knee and ankle, especially if that force is coming from the wrong directions.