Research on infant motor development spans various domains such as reaching, sitting, crawling, and walking; however, the development of sitting on chairs has not been thoroughly examined. In this study, we observed infants’ chair-sitting behavior over the course of one year in a daycare setting to examine flexibility and changes in control strategies. The sitting behavior was analyzed based on the following aspects: adjustment of the distance between the chair and table, accomplishment of sitting (whether the buttocks touched the seat), leg movements, assistance from caregivers, and onset of walking. Focusing on three infants, we conducted a longitudinal analysis of intra-individual changes rather than relying on group averages. Changes in sitting behavior before and after walking onset did not show a consistent trend across all three infants; rather, some aspects changed in child-specific ways. A common sitting form was observed among the three children: standing beside the chair, placing one foot on the seat, and then sliding the foot over the seat to complete the sitting. This process involved exploratory behaviors and showed variations in how the infants attempted to sit. Each child developed a unique method for achieving seated positions on chairs. Furthermore, sitting behavior that initially appeared as part of a continuous sequence from pulling up and cruising became an independent skill after the onset of walking. These findings highlight the dynamic interplay between the intrinsic dynamics, postural and locomotor development, and environmental exploration.
