Not that I disagree necessarily, but to play devil's advocate: kids don't learn any formal grammar rules before they speak their first language fluently.
Well kind of depends what you mean. Kids do years of formal grammar in school here in Germany, the language is hard. Kids take a long time to pick up a language via immersion and they typically don’t need to express any complicated constructs. They also have all their needs met by a caregiver, I know what you’re getting at but it’s impractical for most adults to learn this way.
To be fair, people were speaking German for hundreds of years without any formal education in grammar.
But the key point is that, while it is POSSIBLE to learn a language this way, it is definitely more efficient with some formal training as well, until you can develop the "ear" for it.
> But the key point is that, while it is POSSIBLE to learn a language this way, it is definitely more efficient with some formal training as well, until you can develop the "ear" for it.
1. Kids take about 7-10 years of constant immersion to become fluent in a language
2. Child brains are different from adult brains, and it is likely that the ability to pick up a language in this way degrades significantly after a certain age
I'm not saying it is impossible to pick up a language without being told the grammar rules, just that it's much faster if you do learn them.
> 2. Child brains are different from adult brains, and it is likely that the ability to pick up a language in this way degrades significantly after a certain age.
There is plenty of evidence which counters the latter part of this claim (see Stephen Krashen and the input hypothesis).