Parental linguistic input and interaction style are essential to infant language development. The current study investigates the relationship between Swedish children’s productive vocabulary size and parental communicative adjustments at 18 months (N = 60) and 24 months (N = 61). Vocabulary size is reported with the Swedish adaptation of the MacArthur CDI Words and Sentences (SECDI) while parental communicative adjustments are measured by parental inclination to wait for infants’ vocal communicative initiative and parental inclination to adjust utterance duration to match the duration of infant vocalization. Pauses between utterances and utterance duration of parents and children are tagged in audio recordings of daily-life situations involving parent and child at the family home, such as mealtime, playtime, or reading time. Infants with large productive vocabularies are expected to have parents who are more inclined to wait for communicative initiatives on the part of the infant and to adjust utterance duration to match infant vocalizations. On the other hand, infants with small productive vocabularies are expected to have parents who are less inclined to give room to communicative initiatives and to match input duration to infant production. Small vocabularies are defined by the lowest quartile (0-25%), while large vocabularies are represented by the highest quartile (75-100%) of SECDI scores. Parental communicative adjustments show differential effects on productive vocabulary size at the two ages 18 and 24 months. This indicates a relationship between parental communicative input, as measured in the aspects of turn-taking pauses and duration adjustment, and child vocabulary development.