Immature guys? Why do they do this?

Well, I'm in 8th grade. There's these new kids that just came this year to 7th grade. You see, my school is like all combined k-12th. Anyway, when you're in 7th grade you start middle school and you're basically fresh meat. Anyway, these 4 guys who I guess are buddies or whatever have always hated me. I haven't said anything to either one of them all year. Except, one of them made fun of a physical disability I have. (Erb's Palsy) He got in trouble for it. Well, ever since then whenever they see me near them they point at me and giggle. Or one of them will say to the other, "Hey look over there." and point at me and giggle amongst themselves. It makes me feel terrible. I told my mom and she said that they liked me. I almost laughed, they do not like me like that. If anything, liking me is a joke to them. I'm fat, ugly and I don't think anyone could ever like me like that. I have a lot friends, don't get me wrong. I actually have a lot of guy friends who are really protective of me and have told them to shut up and stuff. It's really immature and really getting on my nerves. Does anyone know why they do this? How do I make them stop?