I had an epiphany! Now I know exactly what bothers me with the innatist perspective on language acquisition. So, children perceive the "grammaticalness" of sentences due to the in-built knowledge. But different languages have different grammar systems, and a grammatical structure of one language will be ungrammatical in another. And this is where I come to a contradiction. Either our brains have a grammar encyclopedia installed, or genes carry the information about particular language, or somtehing does not work here.