I was so busy talking about my own experience I forgot to chime in on the first post. Yes, I would be mad. If I wanted to tell my kids I would. It is not the place for a teacher,other children,or anyone to bust the bubble so to speak. My kids know not to give others a hard time. Accept it for them,disagree for yourself,and then move on.
I would be angry with this teacher,but at the same time realise that this is what happens when we put our kids with strangers for 4-8 hours a day.We are going to have to accept that sometimes those people will say things to our kids that we do not agree with. The teacher ofcourse should know better. I am sure there will be an inservice as a result of this,and teachers will be taught to avoid the subject.