I have a theory that those sounds are what a baby naturally says as their start tgeir vocal journey. So we adapted the words we use to mean mother /father accordingly.

I'd like to point out that children do, in fact, get confused in this way.

When my sister's child (who now uses they/them pronouns) was quite young (maybe three years old? I'm not certain), when something upset them, they would say "oh no wha happen?" because they knew that when their parents responded with concern after they scraped a knee or something, they would always respond with "Oh no! What happened?" So even though the new situation didn't rise to the level of provoking crying or whatever, because they wanted that same level of attention and concern, they just directly asked for that response. It was pretty cute.

Similarly, when they wanted something to happen, they would ask it as a question: "want to make those guys talk?" (which meant "please make believe with me and provide voices for some of these stuffed animals"). Or "want to just bring the bowl down?" (which meant "I'm not sure which candy I would like! please bring the candy dish down so I can pick them by looking at them [and maybe take more than one]"). So they were definitely imitating things their parents said before understanding the full grammar of the situations involved.

Can't remember where I heard this, but I believe the terms themselves evolved around common infant mouth sounds. Hence why so many languages use the term "mama" for mother.

The baby makes random sounds, meaning is ascribed to them by the parents, the baby is given positive feedback and starts to make those sounds more frequently, and then the meaning eventually sticks for the child once they actually begin developing language.

My niece refers to herself as "you" because she doesn't understand that when people refer to her as "you", that isn't her name.

She's 27 years old...

They understand almost everything long before they say their first words.

The very first document my daughter received by mail after she was born was her Tax ID. Thank you, Finanzamt.

Who says say?

huh?

Emphasis, most likely

This is one of those memes you should feel bad about posting OP

The first words from mine were... NO!! LOL

My guess is that understanding language is just a brain thing, and formulating and speaking language is a brain and motor skills thing

You learn the simple things first, and the hard stuff only when you realize you absolutely must learn them.

My son would've learned: "It's Daddy.", "I'm Daddy." instead.