Adult semantic networks show small-world structural properties that are believed to support language processing and word retrieval. The focus of this paper is to understand when these properties emerge in lexical development. We believe that they relate to the rate of word acquisition and vocabulary size. To address this, we examine the connectivity patterns of semantic networks of individual children and compare children on faster and slower vocabulary growth trajectories. The results show that small-world properties emerge early. However, children on slower growth trajectories, who are at risk for significant language delay, do not show these properties. The differences between typical and these so-called “late-talkers” persist, even when vocabulary size is equated. Late talkers’ vocabularies are not only acquired later, but also less cohesively, a fact that may relate to future language processing difficulties for these children. In brief, the results suggest that properties of network connectivity may play a role in early lexical development. Keywords: semantic networks, language acquisition, corpus analyses, late talkers