Yeah, from 4th to 8th grade, kids are just getting to start swearing and knowing that words can hurt people. They tend to go off the handle because it is something new and exciting and everything. But, as this has been directed at you for like 2 years, you should most def put a stop to it. It shows you have a lot of patience and stuff. If kids were making fun of me, there would be a whole Step Brothers Beating Up Kids Montage.
Just beef up, give them a dirty look right in their beady little eyes, and keep going. That's generally how I keep my sister's friends and little cousins at bay. You could also go down the route of Questioning, which will put one child on the spot in front of their peers. This will freak them out and show the rest of them that you mean business.