This right here. I talked with my kid from day one. Not baby speech, but like I would be talking to a young child. Of course there was some baby speak as well, but mostly just keep talking all the time. Sing to them, doesn’t matter if you’re good. Teach them childrens songs. And when they start understanding and doing things on their own - show and explain everything. And always try to remember that they have no reference for anything, everything is new to them, even the most trivial things.