Background Since the outbreak and global spread of COVID-19, countries rapidly introduced a range of preventative measures and isolation protocols to ensure safety, which ultimately led to the implementation of total lockdowns. As a result, children lost access to spaces where they typically engage in physical activity and were required to stay indoors. Objective The objective of this study is to assess the impact of the COVID-19 pandemic on children's physical activity levels and analyze the factors influencing their physical activity during this period. Methods Parents from various Emirates participated in an online survey to evaluate changes in their children's physical activity during the COVID-19 lockdown compared to the pre-lockdown period. The survey included questions about time spent on sedentary activities, general physical activity, and specific play behaviors before and during the lockdown. It also assessed the parents' own physical activity and their involvement in their children's activities. The relationships between these behaviors, as well as demographic and environmental factors, were analyzed. Results The study included 272 parents who completed an online survey about their child's physical activity during the COVID-19 lockdown. Many parents reported significant changes in their children's physical activity and screen time. Specifically, 89 (32.7%) observed a major decrease in physical activity, while 77 (28.3%) noted a minor decrease. Regarding screen time, 79 (29.0%) of parents reported a major increase, and 87 (32.0%) saw a minor increase. Key factors influencing children's physical activity were identified. Most notably, parents' own activity levels had a significant impact on their children's activity (p < 0.001). Additionally, children living in villas were more active than those living in apartments or traditional houses (p = 0.007), and UAE national children were slightly more active than non-nationals (p = 0.023). Conclusion This study demonstrated the significant impact of the COVID-19 lockdown on children's activity and emphasized the importance of parental involvement in supporting their children's activity levels. It highlights the need for increased attention during the recovery phase from this crisis and calls for the development of strategies and guidelines to prevent similar challenges in future pandemics or similar emergencies.