thinking about native languages

I recently started a language class for my 5th language (not programing). It's been a while since I learned a new language, and this time I picked a language that is readily accessible: Korean. I sometimes watch Korean dramas, listen to K pop, and I happen to have a conversation partner who kinda knows Korean but not really.

I was reflecting on all the languages I know and realized that I wouldn't know how to teach languages I picked up natively, but would have no problem teaching a language that I learned non-natively. And that got me thinking about what it means to formally learn a native language, and a non-native language. For instance does it make sense to insist on hiring native speakers?

With native languages, I speak them before I know how to read and write them. My vocabulary and grammar were learned before I could understand how I knew them. There are other definitions of native language, but for this example, it is obvious. A non-native language is a language I had to learn formally. Before going to language class, I couldn't express myself in this language. What is worse is that I have to actively search for a place to apply my newfound language ability.

I wonder if it is impossible now to learn a language using native means since I wouldn't even know how to start picking things up. The closest possibility is to learn a language while needing to use it. In many cases, people pick up a language hoping to eventually use it. It all works.

I tried to read up on how babies learn a language (see the article on Deb Roy in Wired). It seems like parents tend to focus on one thing for an extended period of time. It wasn't a helpful article. I'll have to browse around a bit more. Let me know if you have any good references.