Drive-by 'thoughts to think' post

While searching for something I don't remember now, I've stumbled upon this video (it's about gender presentation in toy advertising), which reminded me of a question I had for some time.

So. Let's suppose that there are children who see those ads and think 'If I=(fe)male, then I (should) like glitter and baking/trucks and adventure'. On the other hand I am pretty certain (as certain as one can be about one's self-knowledge, heh) that there are children who see these ads and think 'If I like baking/trucks, then I=(fe)male' (or 'then I should be (fe)male'). This is all very simplistic, obviously, but. But. Why? How? We learn very early what gender sex we are. I certainly knew I had a vagina when I thought I might be a boy since I like pirates and adventure. What determines which way inner reasoning goes, from actual sex to a gendered idea of preferences or from actual preferences to gender identity? Again, simplistic, but there must be some processes that govern this thing. What are they and how they function, inquiring minds want to know.

And now to the portion of the program where I go about my day and forget to research this stuff for months.