upbringing and norms

http://www.bbc.com/news/av/magazine-40936719/gender-specific-toys-do-you-stereotype-children

well that's a rather interesting experiment
don't know how to link the video but click the link.

Swapping gendered attire on two kiddies, and watching volunteer adults bring toys to them to play
For the male dressed up as a girl, adults brought the more feminine toys,
girls dressed as a male, male toys.
and with both behavioural interaction differences displayed by the adults

ain't that peculiar

says something.