This is the point of the Chinese room, because "speaking Chinese" that is to say manipulating syntax, does not give rise to meaning, the semantics of Chinese.

An elementary school child will have no understanding of language. At all. It won't be able to explain why it builds sentences the way it does or why it thinks certain sentences are wrong or right. Hell even I, after all the education I've had, am writing these sentences purely by feel. English isn't my native language either and I mostly learned to produce reasonably sounding sentences by reading/watching lots of things in English. The school tried to teach me grammar and all those formal "why it is the way it is", but I honestly sucked at it and never cared.

When I want to express myself in English I don't have to "understand" how to correctly construct English sentences. I can't justify why I put the words in the order I put them. People seem to understand and often people can't tell I am not a native speaker. But I don't think I understand English anymore than the Chinese room. There is an actual "English room" made from meaty neurons in my brain that is just used as a machine by my consciousness to convert my thought into "working" English. It's not part of my consciousness however. Just a biological neural net I trained with lots of examples from English TV and English books.

So the idea of proving anything about consciousness using language understanding thus seems pretty useless.

It can't tell myself apart from a dead rock.