The idea is, I think, that the children are born knowing for example that there are words that name things (nouns), words for actions (verbs), and words that describe things objectively or subjectively (adjectives) and with clues about how these words might be fitted together to make sentences giving information, expressing emotion, or giving commands etc., that there are limitations on what grammatical features are possible and the child is born knowing what those limitations are.

Bingley

Bingley