Background: The coronavirus disease-2019 (COVID-19) social-distancing strategy, including 7 weeks of strict lockdown, enabled an extraordinary test of stay-at-home regulations, which forced a sedentary lifestyle on all children and adolescents.

Objectives: To assess the lockdown effect on pediatric weight.

Methods: A retrospective-prospective cohort study at our hospital’s pediatric outpatient clinics following the COVID-19 lockdown. Patients aged 0–18 years visiting the clinic were weighed and previous weight and other clinical data were collected from the medical charts. Weight-percentile-for-age standardization was calculated according to the U.S. Centers for Disease Control and Prevention and the World Health Organization growth tables. Pre- and post-lockdown weight-percentiles-for-age were compared using paired t-test. Multivariate analysis was conducted using linear regression model.

Results: The study was comprised of 229 patients; 117/229 (51.1%) were boys, 60/229 (26.2%) aged under 6 years. Total mean weight-percentile was significantly higher following the lockdown (40.44 vs. 38.82, respectively, P = 0.029). Boys had a significant post-lockdown weight-percentile rise (37.66 vs. 34.42, P = 0.014), whereas girls had higher baseline pre-quarantine weight-percentile of 43.42, which did not change. Patients younger than 6 years had a significant increase in weight-percentiles (39.18 vs. 33.58, P = 0.021). In multivariate analysis these correlations were preserved.

Conclusions: A general weight gain among children was noted, especially in boys during the lockdown, with substantial effect under the age of 6 years. This collateral side-effect should be considered in further quarantine regulations