Early life, environmental, and demographic factors associated with change in toddlers' objectively measured sedentary behaviour between 18 and 36 months of age.

This study examined individual variation in change over time in sedentary behaviour and factors associated with higher or lower sedentary behaviour and change in sedentary behaviour in 110 toddlers from 18 to 36 months of age. Mother/child dyads were recruited into the study when children were 6 months of age. Mothers completed surveys, and children were measured at 6-month intervals to 36 months. Children wore accelerometers for one week at each time point, and height and weight were measured. Growth curve modelling examined relationships between demographic, early life, and environmental factors and sedentary behaviour from 18 to 36 months. Fifty-one percent of the children were boys. The trajectory of sedentary behaviour increased from 18 to 24 months then declined. Children with higher sedentary behaviour were less likely to be enrolled in daycare (p < 0.05), and they engaged in higher TV/electronic media use (p < 0.05). Children with lower sedentary behaviour were more likely to have been breastfed (p < 0.05). Children with higher locomotion scores at 6 months were less sedentary at 18 months (p < 0.05), but this difference diminished over time. Mothers should be encouraged to breastfeed, limit their child's TV/electronic media use, and provide opportunities for their young children to be physically active.