Background: Children are expected to adhere to the recommended physical activity (PA) dose of 60 minutes per day and minimize sedentary behaviors (SB) to stray away from the cardio-metabolic disease risk. However, there is a lack of review of current evidence pointing to the negative physical health effects of the Covid-19 lockdown, with its barriers and facilitators for effective PA implementation in children aged 3 to 13. Methods: Two independent authors conducted an extensive search on five peer-reviewed journal databases for the studies examining changes in PA or SB in children and the potential barriers during Covid-19 lockdown. Results: Of 1039 studies initially screened, only 14 studies were included. Ninety-three percent of the studies were cross-sectional surveys. A 34% reduction in PA was noted while SB, including screen time, increased by 82%. Our review identified potential barriers to the effective implementation of PA behaviors in children at four levels: individual, family, school, and government policies. Conclusions: A moderate reduction in PA and high SB in children during lockdown was linked with obstacles at the individual, family, school, and political levels. Stakeholders should consider the above barriers when designing and implementing interventions to address low PA and SB practices.