First, we have to acknowledge that the term "sex" refers to biology, and your sexual organs. You are born a girl, a boy, or intersex. Therefore, the term "gender" refers to culture and society-- often phrased "social construction of gender." What does it mean to be a man, or to be a woman? What adjectives have you been called recently?
- weak, pretty, timid, demure (dowdy/frumpy, matronly, brazen, coy, slut, whore)
- strong, handsome, burly, macho, stocky, strong (effeminate, queer, weak, timid)
Quick homework, go to Toys-R-Us (or some equivalent) online, and search for toys for kids under 5... there is an option to sort for "girl toys" and "boy toys." Here's my test-- "girl toys" got this doll in the top 10 results, "boy toys" got this in the top 10 results. Pink baby doll, sports car, socially constructed gender.
You see your friend's young kid for the first time, what do you say? "Jane, your dress is so pretty!" or "Mark, you're so tall!"-- would you ever tell a boy that he was "pretty"?
Right there, you answered no. There is no escape from social constructions of gender. We are all victims of the society we are born into. But, we must all work to end these stereotypes of gender-- the manly man and the girly girl. Girls can do anything boys can do. Boys can do anything girls can do. We should never limit our children to dolls and pretend kitchens, or trucks and cars. We should never tell a little boy "you can't paint your toenails, that's only for girls" or tell a little girl "you can't play with trucks, that's only for boys." Just like we should never tell girls that they couldn't be things like doctors, astronauts, truck drivers, breadwinners, or the president; and how we should never tell boys that they can't cry, become a dancer, or be stay at home parent. Think before you speak and before you buy.