Why are people so worked up about a princess party, or anything 'girly' for girls. Yet if a parent organised a pirate party, or superhero party for boys nobody would give it a second thought.
There are gender stereo types because genders naturally tend to veer towards "types". Of course that's broad and general but as someone said, a girl who might want to do something girly is immediately branded as being gender stereotyped by parents, shops, society, teachers, neighbours, anyone who may have ever come in to contact with her. But maybe, just maybe a girl would actually like to play with a doll and pram.
I'm not a girly girl. Never have been. Sometimes I like to wear a dress and make up. 98% of the time I'm in jeans, boots and barefaced!
My daughter has an older brother (and a not particularly girly mother). The hand me downs she wore as a baby when she was crawling around the floor were navy and grey tracksuits!! As soon as she started to walk she automatically gravitated to the pink and fluffy section of any shop we were in! Nothing to do with me and no outside influence.
Lots of girls like 'girly' things. They shouldn't be made to feel wrong or silly for being a "gender stereotype". A boy would not be encouraged away from playing with cars or dressing up as a pirate.
I think this thing of "gender stereotyping" seems to only work against girls. Who, as a results are being made to think that boyish things are better than girly things because they are being made to feel wrong or silly for liking girls things and encourages more towards breaking the stereotypes. I don't see the same effort being put into discouraging pirate parties and tractors as an example for boys.