Coaching issues

Hi Everyone...so looking for advice. It is my 2nd year coaching novice and I am having a major issue with some parents. Apparently there is a small group who constantly criticize and belittle everything I do, they talk behind my back, and also try to get other parents on board with them. I don't need this. I coach the local high school team as well, for over 15 years and I have never dealt with such childish behavior. Any idea how to approach this ???