I teach children with asd in primary. A wide range of language abilities.
Some of my yr 6 are at the stage of a 1yr old in terms of expressive language and communication and some are reading Harry Potter, and can tell you all about it.
I do agree theres a conflict with how we refer to stereotypes and within the feminist issues with stereotypes.
However, at the lower cognitive levels of communication they and we do rely on stereotypes. Pronouns are an area of language that's much more complex and relies on a high level of social understanding.
Children working at a v low level aren't as aware of wider social implications of stereotypes. They also both tend not to have much interest in stereotypical clothing or styles for their own sex, and parents generally (here) dress them to be as comfortable and actually conforming as possible. Also due to that cognitive level have more freedom to choose toys they like.
A child who is beginning to communicate at a level where they may use he or she (often get it confused as my 3 yr old is at the moment) would have it modelled and would usually naturally learn that modelling. (But you find many avoid pronouns and use names as it is confusing)
I've never said "she is a girl because she has long hair." I've only said "she is a girl. So we say she."
In my experience anatomical differences are directly taught at yr 5 and 6 and the children have generally worked out who is a girl or boy, apart from the "core" groups.. But it can be confusing. A few believed a new TA was a man. We must keep clarifying for them.
We use the stereotypes till they're at an age/ stage where the stereotypes can be challenged and they can understand the difference between males and females. The Rachel Rooney book is perfect for that.
These children's worlds are small though and they usually only need to know/ are able to know the names of a few people familiar and close to them.,
This does however highlight how very vulnerable these children are are twisted language and confusing queer blurring of queer language.