The present study examines the amount of input and output in congenitally hearing-impaired children with a cochlear implant (CI) and normally-hearing children (NH) and their normally-hearing mothers. The aim of the study was threefold: (a) to investigate the input provided by the two groups of mothers, (b) to investigate the output of the two groups of children, and (c) to investigate the influence of the mothers’ input on child output and expressive vocabulary size. Mothers are less influenced by their children’s hearing status than the children are: CI children are more talkative and slower speakers. Mothers influenced their children on most parameters, but strikingly, it was not maternal talkativeness as such, but the number of maternal turns that is the best predictor of a child’s expressive vocabulary size.