Physical activity provides positive health benefits for preschool children. The aim of this study is to examine the effect of physical activity videos on the physical activity levels of children aged 4, 5 and 6 in preschool time. Two preschools served as a control group, and four served as intervention groups. The study included 110 children aged 4–6 years, all wearing accelerometers in the preschool for two weeks. In the first week, both the control group and the intervention group carried out their ordinary activities. In the second week, the four preschools in the intervention group used the activity videos, while the control group continued their ordinary activities. The main finding is that the activity videos only increased the 4 year olds’ physical activity in MVPA (moderate to vigorous physical activity) from pre-test to post-test. Furthermore, the results show significantly increased CPM (counts per minute) in preschool among 4- and 6-year-old children in the interventions group from pre-test to post-test. However, the children in the control group did not have a significant change in their CPM or MVPA from pre-test to post-test. Our findings indicate that the use of activity videos may increase preschool children’s activity levels at preschool, but that the videos need to be developed differently depending on the age of the children.