This study aims to explore the impact of COVID-19 pandemic lockdown on household food security and the nutritional status of the children and identify the risk factors associated with it. A cross-sectional study was conducted in 220 households having at least one under 5 children of Narayanganj district in Bangladesh. Household food insecurity, coping strategies and nutritional status of children were the main outcome variables. Multivariate logistic regression analysis was performed to investigate the significant determinants. A total of 93.2 % of households were food insecure, with 32.3% experiencing mild, 18.6% facing moderate, and 42.3% undergoing severe food insecurity. Forty seven percent households used high coping strategies and 93.2% of households consumed less expensive/preferable food as the common coping technique. Logistic regression analysis showed the variables significantly associated with moderate to severe food insecurity were low household income before COVID-19 (AOR = 46.07, CI: 13.68-155.10), more reduction of family income (AOR = 32.47, 95% CI: 9.29-113.41), maternal occupation as housewife (AOR = 7.73, CI: 2.59-23.07), losses of job (AOR = 4.28, CI: 1.31-13.98) and higher family members (AOR = 3.39, CI: 1.07-10.71). The prevalence of stunting, underweight and wasting in children under 5 years of age were 29.0%, 23.4% and 15.6%, respectively. Significantly the independent predictors of stunting were maternal occupation, education, age, household head occupation, child age, and the coping strategy score. Household dietary diversity score was an important independent predictor of underweight and wasting. In conclusion, social safety net initiatives for vulnerable households along with maternal education and employment should be strengthened to reduce hunger and malnutrition.