This paper deals with the use of interjections in early language development and children’s literature with special emphasis on the syntactic role and meaning of interjections in statements and/or verses. In communication with children, children’s poetry and picture books, as well as children’s speech, interjections replace nouns, verbs and adverbs, i.e., they have a different syntactic function which is proven by the examples. Special emphasis is also being placed on the interjections’ function as exclamations in children’s statements and poetry which goes beyond sentence structure. The paper presents different development stages in acquiring first language, i.e., development stages in children’s speech production, and the frequency of using interjections in different sentence functions while mastering speech. Furthermore, it analyzes and provides examples of the use of interjections in children’s poetry from folk oral poetry to contemporary picture books as well as picture books for speech therapy. It emphasizes the influence of a child’s motor development on speech development, as well as the influence of motherese, parentese, i.e., speech which parents or guardians use with their children (baby-talk), and applying games and picture books for speech therapy in reading routines with children. Examples provided in the paper prove the polyfunctionality of interjections in children’s speech and children’s literature.