At 8 months, babies already know their grammar

Even before uttering their first words, babies master the grammar basics of their mother tongue. Thus eight-month-old French infants can distinguish function words, or functors — e.g. articles (the), personal pronouns (she), or prepositions (on) — from content words — e.g. nouns (rainbow), verbs (to drive), or adjectives (green), according to researchers.

Source: At 8 months, babies already know their grammar