A kid doesn't know any different, pink and blue are colours, dolls and trucks are fun toys. However if a parent calls a boy gay for playing with a doll or older kids refuse to let a little girl play football because she's a girl, that's when the idea of gender stereotypes are planted inside kids head and it has an impact on their personality development.
So let kids be kids, otherwise we might have to not only ban pink and blue and Disney but maybe Christmas too.