UNLABELLED: This study aims to examine the effects of physical activity, eating habits, sleep patterns, and media use on children's body composition during the COVID-19 pandemic, as well as the relationship of these factors with sarcopenic obesity (SO). This prospective cross-sectional study has involved 431 healthy male and female child participants aged between 6 and 10 years during the COVID-19 pandemic lockdown period. The daily routines of participants, including their dietary habits, levels of physical activity, and media usage patterns, have been assessed. The anthropometric measurements taken included body weight, height, body mass index (BMI), and skinfold thickness assessments. Body composition analyses have been conducted using the bioelectrical impedance (BIA) method to determine the total body fat and muscle mass as well as the fat percentage. It has identified obesity in 25.2% and SO in 9.5%. Children with SO have had mean BMI SDS of 2.67 ± 0.4 and mean waist circumference of 78.5 ± 9 cm. Fruit consumption OR = 2.68, 95% CI (1.13-6.31), the number of household members OR = 0.54, 95% CI (0.35-0.84), the duration of sitting time OR = 1.17, 95% CI (1.02-1.36)], and junk food consumption OR = 1.27, 95% CI (1.03-1.57)] have been found to be effective in the development of SO. CONCLUSION: The COVID-19 pandemic has had a significant impact on the body composition of children, resulting in an increased prevalence of obesity and sarcopenic obesity. This research highlights the critical importance of engaging in regular physical activity, consuming a balanced diet, and obtaining sufficient sleep, particularly during times of crisis. WHAT IS KNOWN: • Sarcopenic obesity is a complex metabolic condition characterized by reduced muscle mass and increased adipose tissue. • COVID-19 pandemic-related physical inactivity potentially has led to adverse effects on muscle mass composition. WHAT IS NEW: • First comprehensive assessment of sarcopenic obesity development in children during the COVID-19 pandemic, utilizing advanced bioelectrical impedance analysis (BIA) to evaluate changes in muscle mass and adipose tissue. • Systematic evaluation of the impact of sedentary lifestyle and dietary habits on sarcopenic obesity during the unprecedented lockdown period.