Family and educational institutions play a decisive role in learning and strengthening habits related to physical activity and health. School has a specific mission in this scope, especially at the first stage of education. Attempting to answer the question of how schools in practice realise these tasks, a study was conducted on the level of physical activity of pupils in classes I-III of primary school, during their participation in compulsory school activities. The study took into account many conditions, in particular, the organisation of school work during the COVID-19 pandemic. Physical activity of the pupils was measured with the use of Actigraphs GT3X+, known also as accelerometers, and the Steps Per Minute Test. The study covered pupils (N = 159) aged 7-9 years, who attended classes I-III of several schools in the region of Eastern Poland. The results of the study indicated that the level of physical activity in most of the examined children was low, which may be a limiting factor in their overall development. Accordingly, the writers suggest that during the coronavirus pandemic teachers urgently need to work out new forms of physical activity for children.