preschoolers from low income families have been exposed to a lot less language than their middle class peers, but i am guessing that it is more the education level of the parents than anything. Or, also that such families tend to see parenting and child enrichment as more of a luxury – either because they are so tired after working two jobs or because they are so dysfunctional that they cannot consider their children’s language development because they are barely surviving themselves.
But, as your case points out, that is only on average. That is why we have kids that are gifted from these same communities. Biology does also have an impact on language development, etc. that is also why some wealthy families have children with language and other disabilities.