The paper presents data on statistical and semantic analysis of speech texts produced by children and adults interacting with their parents and an experimenter. Mothers’ speech addressed to infants and children of the first three years of life was analyzed. Speech of typically developing children, children with Down syndrome and autism spectrum disorders, adults with atypical development, and experimenter interacting with them was investigated. Differences between the groups in the number of significant and unique words in texts and in the frequency of words reflecting the emotional state were revealed. The expansion of the child's lexicon and lexical emotional space through the interaction with an adult was shown.