My son, at age three, when asked by his mother where I was, replied, "He's on the damn couch." Perfect inflection, and everything. I didn't stay on the couch long after that...
My daughter, when she was in 2nd grade at a parochial school, was called in for saying, "Move your butt out of my way." We were called in, too. They told us they would prefer that she didn't use the word, "butt." I said, "Well, it's a shortened form of the proper word, 'buttocks' - would you prefer she'd used a vulgarity like, 'ass' instead?" The looks on their faces were priceless.