Parents teach their children the system of language and teachers teach children all the rules and how to speak correctly. To think parents can teach their children how to speak is ludicrous.
Language acquisition occurs in all children in the same succession of stages.
2 Language is acquired in early childhood and adults have few memories of the intense effort that went into the learning process any more than remembering when we learned to take a first step. Adults have difficulty dissociating their memories of school lessons from those of true language learning. FACT 4 Rules learned in school were only conventions of an educated society which are arbitrary to learning by anyone, at anytime, and any place. Every adult can create or understand an infinite number of sentences never heard before. We do not experience everything we know.