Remember how it was to have someone taunting you after school? Any bullying going on in your neighbourhood now? Is one of your children relentlessly teasing another kid nearby? Bullying is a very real problem, and can cause physical as well as emotional harm.
If you suspect that your children is bullying others, you should address this behaviour immediately. In some cases, an over zealous parent may think the child is merely standing up for him or herself, but that is short sighted.
Aggressive behaviour that is slowly manipulating another person's mind is a form of abuse and comes from a troubled, even devious, mind.
I have to repeat once more that when such instances are apparent, you must look inward first. Perhaps mom or dad is not showing the best example. It may be difficult to determine or discuss at first but it must be done. You may need to admit to mental or physical abuse in the home.
Unfortunately the bully is a focal point of so many potentially damaging behaviours. The bully is liable to do anything that suits the situation. This, in and of itself, makes the taunting behaviour so difficult to treat, but as a start it may indicate a severe lack of real care and affection. The child may get lots of attention but not adequate affection.
By observation, I have noticed some correlation between body type and bullying with the more rotund boys, at least, picking on thin ones. This could point to a strong rebellion and helplessness with respect to their own obesity. And it is certainly something mom and dad can focus on, vigorously.
I will research more on this matter as time progresses, but for now I urge you to keep a watchful eye, and begin the discussions as the need arises.