I almost cried reading this- you need to talk to the administration of this school! This is unfair to your son, and to you! I don't know what to say except that the administration should know about this- her contract comes up every year, and they can not renew it if she is being harmful to children!
Good luck!
This is a sad issue maybe the teacher doesnt remind children to take a "potty break" from your post I would be inclined to find your child another school as this teacher does seem to have a problem and your son is rightly upset, have you spoken to the principal of the school , it is important to put your childs welfare first , look for another school and definatly put in a complaint about this teachers attitude, for other childrens sake..Good luck let us know what you decide to do..