Mean racial remarks still happen

First mean racial experience: at Target tonight our son Dillon (11 years old chronologically but about 6-7 developmentally) was 2 aisles over from me. I heard some giggling and looked over. Three other boys, looked about 12 years old, came over and were playing around. I kept waiting on Hudson a few more minutes. Pretty soon Mike and Dillon came walking up. Mike had rounded the corner of the aisle where Dillon was. The other boys were close in his face saying fake Chinese words "Ching Chong Ching Chong". When they saw Mike they took off running!! Poor sweet Dillon had no idea what to do or really what they were doing. He was bothered by them being in his face. Mike walked all over that store looking for the boys(they should be glad he didn't find them!). I was fairly surprised at these boys making fun of a Korean child. Our adoption agency(the best ever...Dillon International) teaches parents that children who were adopted and are of a different race than the parents don't struggle so much with adoption issues as they do with identity and race.  We've just never experienced this type of negativity before.  
The most distressing aspect of this was not the stupid racial remarks.  We are most concerned over how defenseless Dillon is and that he can't relay a story because of the speech disorder.  If something more serious happened and we were not around, I shudder to think of it!  I'm seriously considering putting him in Tae Kwon Do or Karate to learn some self defense and confidence.