Characterizing the frequency and content of speech from other children in daylong recordings of infants’ input

Infant’s language development is inherently tied to their linguistic input, but the majority of research investigating infant’s input has focused on adult caregiver speech. However, children do not exclusively interact with adults. In the US, 80% of children’s households include additional children. The focus on adult caregiver input thus does not fully capture the experience of the majority of children. We quantify infant’s experiences with speech from children, measuring its frequency and content. We find that speech from children is a common feature of the input for infants with older siblings, occurring once every minute. Analyses of content find that children produce the same words more often (lower type-token ratio) and shorter utterances overall, and that their speech contains earlier learned words and more nouns. Speech from children however does not vary from speech from adults in average word frequency or in iconicity. We highlight the importance of considering speech from children for infants with older siblings in our theories of language development.