Children Learn to Signal Shifts in Joint Tasks Earlier Than Continuations

Coordinating joint actions requires participants to maintain moment-to-moment alignment as they progress through multiple tasks towards a shared goal. This creates the coordination problem of negotiating whether participants intend to continue to the next step in a task (i.e., make a horizontal transition) or shift to the next task (i.e., make a vertical transition). Language plays a central role in resolving this problem by enabling participants to distinguish horizontal and vertical transitions with specialised coordination markers (words like yeah, uh-huh, okay). Coordination markers constitute an important component of procedural coordination in adults; however, little is known about how children acquire the ability to use them. Here, we addressed this gap by investigating (1) how 4–8 year-old children speaking Swiss French and Vietnamese deploy coordination markers in peer interactions and (2) how the acquisition of these markers relates to the development of perspective-taking skills. In an experiment, we tested how N = 266 children and N = 158 adults from Switzerland and Vietnam navigated the joint task of LEGO model construction in visible (no barrier) and hidden (separated with a barrier) conditions. Our findings show that children acquire the ability to signal vertical transitions and the linguistic markers associated with them earlier than horizontal transitions. From early to middle childhood, there is a notable increase in both the frequency and diversity of coordination markers produced by children; however, their productivity remains limited compared to adults. Besides age, the acquisition of coordination markers is linked to the development of perspective-taking abilities, which enable children to flexibly adapt their use of coordination markers in response to changes in mutual visibility. Our study highlights how emerging socio-cognitive capacities support the acquisition of coordinating conventions across two typologically diverse languages.