The main purpose of the study was to determine 3-year-olds' physical activity levels and how these vary across season, gender, time of day, location, and the physical and social environment in childcare settings in Finland. A modified version of the Observational System for Recording Physical Activity in Children-Preschool (OSRAC-P) was used to measure physical activity levels and contextual variables (e.g., group composition, prompts) of children attending childcare centres. In total, 81 children (42 boys and 39 girls) were observed in autumn and in winter. Three-level linear regression analyses were used to assess differences between the seasons in the association between the context variables and physical activity. During the observations, the present sample of children was mostly sedentary in nature, engaging in moderate to vigorous physical activity in only 2% of all observations. The results further showed a significant difference between season and the children's physical activity levels: in winter, the children spent significantly more time in sedentary-level activities and less time in moderate to vigorous physical activity than in autumn. The present sample of children was physically more active outdoors than indoors. Boys showed significantly higher physical activity levels than girls. The majority of the observations did not include any oral prompting. We conclude that childcare centres offer good opportunities to increase children's physical activity. Interventions should focus on enhancing children's outdoor time, free play, and positive prompting and encouragement by teachers.