Sorry for just dropping in on the thread. I agree that your son seems to be unfairly treated here but it did make me think a very upsetting thought.
It's really concerning that a 3 year old could say that word in context and the school should definitely be taking things further by talking to her parents. They both need to know it's an unacceptable word, but to be able to use it in a sentence, she must be being exposed to something, even if it's only tv.
WEDDING DATE 9TH NOVEMBER 2007