The aims of this study are as follows:

• The primary aim is to investigate the relationship between changes in screen media use with changes in non-sedentary time (time, min/day, spent in activities other than lying and sitting) during leisure (outside nursery) from baseline to 18-month follow-up.
• The secondary aim is to investigate the relationship between changes in screen media use and time (min/day) spent in specific daily activities (lying, sitting, moving, standing, walking, and running) and changes in moderate-to-vigorous intensity physical activity during leisure.

The current study is a secondary, observational investigation of data from The Motor Skills in PreSchool (MIPS) study. The MIPS study was initiated in 2016 and included preschool children (3-6 years of age) attending public preschools in the Municipality of Svendborg, in Denmark. A subset of the preschools included an intervention component, whose aim was optimization of motor skills. In this study, the children's screen media use was assessed via questionnaire and physical activity was assessed using two Axivity AX3 (Axivity Ltd., Newcastle upon Tyne, United Kingdom) triaxial accelerometers - one placed at the hip and one at the lower back - at both baseline and at 18-month follow-up. Time spent in distinct activity types (sitting, moving, standing, biking, running, walking, and lying down) are determined from the acceleration measured with the thigh worn device. In addition, data on relevant covariates was also collected. Having data on both exposure and outcome at baseline and follow-up renders detailed longitudinal assessments possible. Furthermore, daily schedule (proxy based on reporting by parents and pedagogical personnel) information on the children introduces the possibility of domain-specific analyses of physical activity, as we can time annotate the data into different sections of the children's daily routine.

Inclusion:

- All children who at the time of recruitment attended public preschools in the Municipality of Svendborg

Exclusion:

- None

3-6-year-old children attending public preschools in Municipality of Svendborg at the time of recruitment (fall of 2016), and their parents