Words out of the mouth of babe's

Jordan has learn't some very descriptive words since attending his "Montessori" programme here in Melbourne. It started when we were away in Ecuador and after the initial shock of saying these words to his Nanny & Ba, we haven't heard them again until recently. What amazes me is that he says these words as if they are like any other word, which to him I guess they are. He doesn't actually use the words as such, he tells us he knows some naughty words and then out they come along with "liar, liar, your pants are on fire" which he also classifies as a naughty word. He is also very quick to point out that he doesn't say them, he is just telling us what the boys at school say!!!! We try NOT to make much of an issue but at the same time explaining that these aren't nice words and we don't use them in our house BUT Jordan knows this and for some reason he is just looking for a reaction or testing his boundaries again. He has obviously put a lot of thought into these words as he will tell you that it starts with the letter "f". At times it is all I can do to keep a straight face just from the sheer way they are spoken and the shock of this language coming out of my little boys mouth....... I do hope this phase ends very quickly!!