It's important to understand how children typically develop, especially when trying to help children who are developing atypically.
Most of my students are Autistic, but all of them at least have language delays. I sometimes get stinkeye from people who wonder why I spend so much time "just playing" with their child. I play with them because that's how children learn first, and I narrate what we're doing for the language aspect. I also use sign language, expose them to picture communication, and try to expand their interests.
I learned sign language back when I started my Masters in Special Ed and taught for a year in my 20s.. Kids can have all kinds of speech, language delay and non-verbal disorders. My thirty five year old daughter has c.p. and depending who you talk to is on the autistic spectrum or has non-verbal learning disabilities. Tests and terminologoes are constantly changing.