Tell that principal it's inexcusable to humiliate you in public. She owes you a big apology. She also isn't a good role model for the kids.
It might make it easier for you to explain to the kids that you had surgery on your tongue and some of your words might sound different. Kids are usually very accepting if you tell them what's going on, unfortunately it's the adults who are usually the cruelest. I know my husband had to tell a lot of people in the courts what had happened so that they would be more understanding. Sorry you had to go through this
Good luck