While much work has emphasized the role of the environment in language learning, research equally reports consistent effects of the child's knowledge, in particular, the words known to individual children, in steering further lexical development. Much of this work is based on cross-sectional data, assuming that the words typically known to children at "n" months predict the words typically known to children at n+x months. Given acknowledged variability in the number of words known to individual children at different ages, a more conclusive analysis of this issue requires examination of individual differences in the words learned by individual children across development, that is, using longitudinal data. In the current study, using longitudinal vocabulary data from children learning Norwegian, we ask whether the phonological connectivity of a word to words that the child already knows or words in the child's environment predicts the likelihood of the child learning that word across development. The results suggest that the early vocabulary grows predominantly in a rich-get-richer manner, where word learning is predicted by the connectivity of a word to already known words. However, word learning is, to a lesser extent, also influenced by the connectivity of a word to words in the child's linguistic environment. Our results highlight the promise of using longitudinal data to better understand the factors that influence vocabulary development.