This study examines the development of children’s ability to introduce new narrative discourse referents. Children 7, 9 and 12 years of age and adult speakers of Greek produced written narratives based on a picture series. The results show that children do not achieve appropriate form-function mappings until the age of 9. The ability to encode a new entity using the appropriate forms in Greek is completed at the age of 12. Moreover, as age increases, speakers tend to place the indefinite NPs introducing a new discourse referent before the verb, mainly in event reporting sentences, rather than after the verb in presentative structures. This shows that with increasing age, speakers tend to introduce the new entity as part of an activity rather than just to denote the existence of an entity in discourse. Finally, syntactic complexity of the introductory NPs increases with age. Adults use more complex NPs that denote characters’ motives and clarify the actions they will perform later in the story. This kind of referent introduction indicates the ability to create a complete mental representation of the story, which seems to develop during school age and is not completed until the age of 12.