Kittens are hard to sex. Its a matter of just a little space or a hole and a dot vs a hole and a slit.
This diagram may help you
http://www.indiapets.com/cats/articles/carta02.htm
But in newborn kittens even experts can be fooled. You may have to wait a little bit before naming them based on their sexes!
This site has pictures of actual kittens
http://www.mystic-tree.com/kitten_sexing_guide.htm
Hope this helps you!
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