Early language acquisition relies on the successful communication of specific word meanings when speaking or encoding labels. Here, we tested for evidence of this communication within the parallel functional neural activation that occurred for adults and children as unfamiliar objects were labelled by the caregiver. Measuring event-related hemodynamic responses with functional near-infrared spectroscopy (fNIRS) simultaneously recorded from both individuals, we compared cortical responses that were time-locked to spontaneous instances of object labelling during openly structured interactions. Most notably, children’s responses differed between words learned and not learned in the right posterior temporal cortex, with relatively greater positive activation when children were not learning. The findings bear relevance to investigations of coordination between speakers and listeners during word-learning interactions