If you are convinced that all these kids are telling the truth, I would meet together with all these kids' parents and discuss a unified plan of action. First, I would collect as many of these name-calling incidents from the kids as possible, in as much detail as possible (dates, times, circumstances). Next, I would schedule a meeting with this teacher. All parents should attend this meeting. At this meeting, I would present the teacher with your written documentation and ask her to respond. Depending upon her response and the satisfaction you receive, the parent group will decide how to proceed further. If you do not receive satisfaction, take it to successive administrative levels until you gain satisfaction - principal, superintendent, school committee.
Reassure your children that you will prevent this teacher from punishing them in any way for their reports of her treating them inappropriately. Praise them for having the courage to speak the truth when it comes to unfair and unkind treatment. Kids should never receive this type of treatment from any adult, certainly not from the teacher entrusted with their education and social and emotional development. Give me an update on your progress.