Assuming an interactionist perspective of development, it is believed that in the process of acquisition and development of language, biology, nature and culture can not be considered as separate elements within human development. Thus, it is assumed that the contact with members of their linguistic community and, especially, the maternal figure, are of fundamental importance for the development of children s language. The present longitudinal study sought to investigate, from syntactic and semantic aspects, the role of maternal speech in this process. For this, four mother-baby dyads - one girl and three boys - were filmed once a week for forty minutes. The maternal speech was transcribed and analyzed, as well as the development of the baby s language, which was measured through the MacArthur Inventary of Communicative Abilities. With the results, some similarities and distinctions between the dyads were observed. There was a predominance of affirmative maternal emissions for the four dyads studied. Negative emissions were the ones that least appeared in maternal speech. On the semantic aspects, we identified the predominance of maternal speech related to the context, followed by speech related to the child and, finally, the speech related to the dyad, in all the dyads observed. In addition, there was a significant increase in the number of words produced by the participating children over the six months. It is believed that this study can collaborate and add in the literature regarding the development of children s language and, mainly, contribute with data from the Brazilian context on the role of maternal speech in this process.