‘Gender identity‘ is just a fancy way of saying sex stereotypes,
Actually, no, the research in young children is about how they come to understand that they are a girl or a boy so it's not a way of saying "sex stereotypes", it's more like understanding what a dog or a cat is.
Children would still understand that they are human, as opposed to feline, and that they are a boy, as opposed to a girl, if we had no sex stereotypes (at least, I think they would, but we'll likely never know!). They just wouldn't base it on what clothes they like and what toys they play with.