This Conference places itself within current debates on the origin and nature of children's language competences. The issues addressed concern more particularly the emergence and development of two central categories of linguistic systems: Nouns and Verbs. At the end of their first year of life children talk in single word utterances to communicate meanings and intentions. Around three years of age, they have acquired enough linguistic knowledge to produce grammatically appropriate utterances for the same purpose. The development of grammaticality - or grammaticalization - of utterances is a central process showing that language is not only a way to communicate meanings and intentions but has properties specific to an organized system. Understanding how the processes of grammaticalization take place during the second and third year, and how they progress and are enriched by further development, is fundamental for a theory of language acquisition in general, and for a greater understanding of typical and atypical development, in particular. In this Conference results obtained within two research projects supported by the ANR, LANGRAMACQ (directed by D. Bassano) and EMERGRAM (directed by E. Veneziano), will be presented and discussed. The main issues will concern the emergence of the Noun and Verb categories within a language system under construction, the nature of the subject's knowledge at different developmental periods, and of the processes of acquisition. The two projects deal with these issues basing themselves on developmental and cross-linguistic approaches. They ally the study of early comprehension and production, as well as analyses of late developments (first and second language acquisition in adult learners). They bring together experimental and fine-grained, scientifically-sound methods of analyses of corpora. They plead for the usefulness of models, e.g., nonlinear dynamic systems theory, for a better understanding of the dynamics of development.