The purpose of this study was to determine the relationship between sound change and lexical structure in two children with functional phonological disorders. Specifically, the question of how sound change infuses through the developing lexicon was addressed. A chronology of phonemic acquisition for the children who participated has previously been documented. These archival data were now extended to evaluate lexical change relative to sounds acquired. Lexical change was examined through the parameters of neighbourhood density and word frequency. Results of this study revealed two converging patterns across children: (a) for each child there was one parameter (neighbourhood density or word frequency) of lexical change which held across all sounds acquired, and (b) for each child the alternative parameter patterned differentially by sound. This variability in lexical change was hypothesized to be associated with the relative degree of feature specification of the sounds acquired. This has theoretical implications for the overlay of phonological and lexical structure, and clinical potential for remediation of phonological disorders.