"Gender is troublesome for young kids. When my daughter was three her guesses about men/women were about 75% correct. She thought grandma was a man. She was very distressed to find out she was wrong about her guesses and the whole man/woman game spun her into a brief period of hyperfeminine dressing.
Some of the problem is captured by the following joke from England. A young boy is shown a picture of a naked man and naked woman, and he is asked to identify the man and the woman. His reply: "How can I possibly tell? They don't have their clothes on!""
Joanna