Look between their legs. If it's a boy, you will see a penis, if it's a girl, you will see a vagina. Then you will be sure that they have differences. Also, everybody is different, as far as personality, looks, eye colors, and everything like that, so no, you can't say their exactly the same.
If you do that, it'll be very obvious which is which. See that stuff between their legs? That's what determines if they are male of female. That's just the main one, but there are a few other differences too: Facial structure, muscle mass, general body shape. However, those latter ones are more of general trends. The first one is the one that makes or breaks it.