Children fast-map new words to their referents early on but do not show robust retention until much later. This paper examines whether children’s interest in a natural category relates to retention of newly learned words in that category. German-speaking 24-month-olds and 38-month-olds (n = 88, 41 female) were trained on novel word-object-associations from different categories. Pupillary arousal and parental reports served as indices of interest in the objects and categories presented. Recognition and retention were tested directly after exposure, five minutes later, and 24 hours later. Both younger and older children showed successful word-object recognition and retention. Furthermore, interest in the category modulates young children’s recognition and retention of newly learned word-object associations from semantic categories across ages.