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This study focuses on the role of maternal speech in dialogical formats in picture book-reading by two twin child-mother dyads (one boy and one girl) between the age of 15 and 26 months. The results indicate that the identified structures are rather short and flexible, far from the ordered and strict model of Bruner. The most used is the one-word structure technique: “isolated name or designation.” Scaffolding strategies employed by the mother take into account the nature of the dialogical behaviors of two twins since as soon as the child is able to designate by pointing (i.e. over 18 months), the adult employs imitative repetition. This strategy appears to play a key role in the lexicon acquisition process. It is also used by each child who, over 21 months, refers to the adult model to increase their lexical stock.