In this corpus study, it is asked whether young children speaking European French build their early syntax around grammatical or lexical words. Specifically, the study examines the relationship of grammatical and lexical words in three types of syntactic structures (determiner--noun, pronoun--verb and subject pronoun--verb). The corpus included 315 samples from children aged 24--48 months, a period of rapid growth in grammatical morphology and syntax. The results of a series of stepwise multiple regression analyses indicate that prepositions and auxiliaries explain the unique variance in determiner--noun and determiners and prepositions explain the unique variance in pronoun--verb and subject pronoun--verb combinations better than lexical categories. All these strong predictors support the view that grammatical words guide and facilitate syntactic knowledge. Early grammar is based not on a lexicon but on basic grammatical relationships that young children build gradually, making use of the formal distributional properties of their native language.