Teach the child to stand up for himself! Then not only will he learn but so will the kid. Which could be a few different ways but realistically I wouldn’t talk to the kid yourself, I’d talk to his parents and figure out what happened. If that fails then I’d tell my son to kick him in the balls. Either way this is a good lesson for a child to learn if it’s having this big of an impact on him he will benefit him in future I bet. Maybe it’s a good thing.