Introduction:
Regular physical activity and compliance with the guidelines for using electronic devices have an important impact on health and quality of life as well as the healthy development of children and adolescents.

Aim of the research:
To validate the author’s questionnaire used to assess physical activity of children aged 5–14 as well as to compare the level of physical activity of children with Down syndrome (DS) with their peers without this syndrome.

Material and methods:
A survey was conducted among 48 parents of children with DS and 55 parents of children without DS. The questionnaire was validated by determining its repeatability and determining the values of the k coefficient. The comparison of the level of physical activity was made using the Pearson’s χ²
Results:
The comparison of the results obtained in the first and second study did not show significant differences in children with DS and without DS. The results obtained in both studies (κ ≥ 0.81) were consistent. It was found that children with DS spent significantly less time on physical education classes and team games, while spending significantly more time on doing gymnastics (p < 0.05).

Conclusions:
The author’s questionnaire can be considered an accurate measurement tool that can be used both to test the level of physical activity of children with DS and children without genetic disorders. More children without DS than children with DS (76% vs. 60%) comply with the recommendations for moderate and intense physical activity. Significant differences were also noted in relation to the time allocated to particular forms of physical activity.