In recent years, psycholinguistic studies have built support for the notion that formulaic language is more widespread and pervasive in adult sentence processing than previously assumed. These findings are mirrored in a number of developmental studies, suggesting that children’s item-based units do not diminish, but persist into adulthood, in keeping with a number of approaches emerging from cognitive linguistics. In the present paper, we describe a simple, psychologically motivated computational model of language acquisition in which the learning and use of formulaic expressions represents the foundation for comprehension and production processes. The model is shown to capture key psycholinguistic findings on children’s sensitivity to the properties of multiword strings and use of lexically specific multiword frames in morphological development. The results of these simulations, we argue, stress the importance of adopting a developmental perspective to better understand how formulaic expressions come to play an important role in adult language use.