Abstract
Previous research has suggested that infant motor skills may be affected by older siblings, but has not considered whether this is due to specific characteristics of the older sibling, or of the quality of the sibling relationship. The current study used a longitudinal diary method to record infant motor milestones from 23 infants with older siblings, along with parent reports and standardised assessments of motor skills. Parent reports of the older siblings’ motor skills and the sibling relationship were also collected until the infants were 18 months old. The motor skills, age, and sex of the older siblings were not significantly related to any measure of infant motor development. A significant correlation was revealed between perceived agonism between siblings and infant fine motor skills at 18 months, suggesting the importance of considering reciprocal effects of motor development on sibling relationships. Overall, the suggestion that older siblings may provide a good model of motor skills for infants is not supported by the current data. In the future it will be important to assess the dynamic interactions between different factors in predicting infant motor development, allowing early identification of motor difficulties, which could impact other areas of cognitive development and health.