Research on the early lexical-semantic system has described how toddlers organize word representations based on semantic and phonological features. This study is a longitudinal investigation of the development of this organization during infancy. Middle-high socioeconomic status Mexican toddlers (n = 28, 15 female) were presented with a preferential looking task using an eye-tracker at 18, 21, and 24 months of age, manipulating semantic and phonological lexical links. The experimental task consisted of presenting an auditory label, which was phonologically or semantically related or unrelated, with a displayed target image. Mean proportion of target looking, time-course of fixations, pupillometry, and vocabulary network analysis were used to describe the properties of priming effects. The results showed that phonological priming developed earlier than semantic priming, and that they were produced by behavioral interference. In addition, pupil dilation showed differential use of cognitive effort in critical developmental periods. Finally, the density of vocabulary networks correlated with semantic effects, and vocabulary size and local network features with phonological effects. These findings extend our understanding of the development of the lexical-semantic system during infancy.