Well for starters the theory is that Crocodile used to be a woman a long time ago, not that he still is one. You make it sound like he is just some kind of crossdresser.
Secondly that picture of him as a child really doesn't change anything. Agreed if I originally would have to put a gender on it, I would say he looks like a male child, however that doesn't mean anything as he's still a child. When Koala was introduced, there was a lot of confusion about her gender, but there is little doubt that she's a woman now that she's an adult. That Crocodile would look like, or intentionally tried to look like, a man when he was little makes sense if Ivankov indeed changed his gender. If the latter is truly the case, well then Crocodile really doesn't seem to have hated it and possibly it was even done on his own request either because he always wanted to be a man or because he already looked like a man, both of which can explain his masculine appearance as a kid.
The truth is the moment you take into consideration that he might have been a woman, you can see him in that picture as a girl just as easy as a boy. The theory that Crocodile was a woman still very well stands and has a decent amount of credibility, something that picture doesn't change in the slightest.
