Children’s speech becomes longer and more complex as they develop, but the reasons for this have been insufficiently studied. This study examines how changing linguistic choices in children are linked to interactive factors by analysing Who-question sequences in Japanese child–caregiver conversations. The interactive factors in focus are progressivity and balanced joint activity, which are core aspects of conversational interaction. Our analysis reveals that as children respond to Who-questions, their responses grow in length and multifunctionality. This growth is positively associated with progressivity, namely a quicker completion of the question sequence, and reduced functional load in the interlocutor’s contributions, resulting in more balanced joint activity. These findings suggest that children adapt their linguistic choices by observing and aligning them with their interactive goals in conversational sequences.
