How do French children acquire the grammatical system of their native language so easily? Many hypotheses have been put forward and experimentally tested to solve this mystery. Generative theories argue that grammar is a universal and innate ability ready to be instantiated after birth. Within this framework, grammatical development is seen as a process whereby universal grammar gradually settles into the language-specific structures of the linguistic input that children receive in the first years of life. In the last decades however, many researchers of child language development have suggested other explanations. Current functional-cognitive research (cf. Langacker, 1988, 2000; Bybee, 1995, 2002; Elman et al., 1996; Tomasello, 2003; Diessel, 2004), proposes a usage-based approach to first language acquisition, where grammar is shaped by usage, and linguistic constructions are taken from parental input and gradually generalised by the child. Usage-based theories thus consider grammatical development as a dynamic process which emerges and evolves, in parallel with cognitive and psychological development, through the use of symbolic patterns which consolidate into grammatical constructions.