> even at a few years old males prefer to play with traditionally masculine toys and girls the opposite
A gendered toy preference has been demonstrated in infants at 3-8 months (!!) using eye tracking software[1]. To make matters even weirder, the same gendered toy preference has also been demonstrated in rhesus monkeys[2] and vervet monkeys[3].
From [2]: "We present here striking evidence of a sex difference in rhesus monkey preference for human gender-stereotyped toys paralleling that reported in humans, suggesting that gender differences in toy choice may reflect evolved sex differences in activity preferences not primarily resulting from socialization processes."
[1] http://link.springer.com/article/10.1007/s10508-008-9430-1