Our goal was to explore the potential continuity between motor activity observed in early social situations and communication development. Thirteen infants between 4 and 6 months of age were observed in daycare centers, either on their own or in dyads, and in two postural conditions: lying on a playmat or seated in bouncers. Infants were found to modify their posture, movements and gaze behavior in dyadic situations compared to situations alone. Moreover, the bouncers facilitated visual interactions while the playmat favored the production of hand movements. This work highlights the need to analyze multimodal characteristics of interactions and to add posture variations as a key variable to better understand how infants develop communicative intention toward their peers.