This study tests the claim that children acquire collections of phonologically similar word forms, namely, dense neighborhoods. Age of acquisition (AoA) norms were obtained from two databases: parent report of infant and toddler production and adult self-ratings of AoA. Neighborhood density, word frequency, word length, Density×Frequency and Density×Length were analyzed as potential predictors of AoA using linear regression. Early acquired words were higher in density, higher in word frequency, and shorter in length than late acquired words. Significant interactions provided evidence that the lexical factors predicting AoA varied, depending on the type of word being learned. The implication of these findings for lexical acquisition and language learning are discussed.