This chapter examines how children develop the specific means of argument realization that distinguish K'iche', Mam, and Ch'ol from one another. Mayan languages have different means of realizing the semantic roles of agents and themes. K'iche' speakers use pronouns or noun phrases to express both agents and themes, whereas Mam speakers use nominal classifiers or noun phrases. However, Mam speakers also express both agents and themes in relational noun phrases. Ch'ol has no nominal classifers and uses pronouns to focus on an agent or theme. The chapter first considers the types of overt arguments that children produce for the individual languages before comparing their use of verb arguments. It shows that Mayan children demonstrate an early awareness of polysynthesis in their target languages.