I have noticed this about people I know that have good vocabularies and were top students when they were young: Their fathers don't do baby talk. When I've seen their fathers interacting with young children, they talk to them as young adults. Is this a known correlation or is my sample size too small?
When I was a kid one of my teachers asked me if I'd gotten a boo-boo. "No," I told her, "It's an injury." My parents always spoke to me as an adult. I'll leave it to you to judge how well it turned out.
That is, except me when I was six... My parents would go to a school meeting and the teachers and other parents would be surprised -- "Oh, you don't speak in written language like your son?".
I guess I had been spending quite a bit more time with books rather than people.