Don't feel bad. young children view an adult female as a mommy and a male as a daddy. Heck my 4 yr old told me a Daddy teaches them Gym at school. I refer to myself as Ms Melly but my DCK's all started off calling me mommy because thats what my DD calls me. now it is a mix as they grow and i'm sure they will stop eventually. My DCG called me mommy and her own mom Mama. so she was differentiating between us.
My Daughter went to home daycare for a short period and called her provider Kelly well Kelly's own Daughter called her Kelly instead of Mommy so it can go both ways
I also try not to answer to mommy but its second nature isn't it?
Maybe be a bit more firm with the older ones and say that around the new kids they need to refer to you as Miss E.