Two experiments examined the effects of phonotactic probability and neighborhood density on word learning by 3-, 4-, and 5-year-old children. Nonwords orthogonally varying in probability and density were taught with learning and retention measured via picture naming. Experiment 1 used a within story probability/across story density exposure context. Experiment 2 used an across story probability/within story density exposure context. Results showed that probability and density interacted to create optimal learning conditions. Specifically, rare/sparse sound sequences appeared to facilitate triggering of word learning. In contrast, the optimal convergence for lexical configuration and engagement was dependent on exposure context. In particular, common sound sequences and dense neighborhoods were optimal when density was manipulated across stories, whereas rare sound sequences and sparse neighborhoods were optimal when density was manipulated within a story. Taken together, children's phonological and lexical representations were hypothesized to be interdependent on one another resulting in a convergence of form characteristics for optimal word learning. (Contains 4 tables.)