This clearly isn’t a kid problem, and I don’t see how this happens without the tacit (or express) approval from adults.
If the taunts are such that the denigrated players walk off the field, why didn’t the offenders’ coaches (and parents) intervene? If I were a coach and my players or fans did this, I would immediately forfeit the game, and demand that the team find a way to try to make amends. If I were a parent in the stands, I would harass the coach and make my child apologize on behalf of his or her teammates/schoolmates, whether my child participated or not.
Who are these people?