Child malnutrition remains a pressing public health issue in Bangladesh, worsened by the socioeconomic consequences of the COVID-19 pandemic. Identifying nutritional status and its associated factors among children under five is critical to guide interventions.

A hospital-based cross-sectional study was conducted from June to August 2021 at the Institute of Child and Mother Health (ICMH), Dhaka. A total of 543 children aged 6–59 months were selected using systematic random sampling. Data were collected via a pretested semi-structured questionnaire and anthropometric measurements following WHO standards. Nutritional outcomes (stunting, wasting, underweight, and MUAC) were analyzed using descriptive statistics, chi-square tests, and multivariate logistic regression.

Among the 543 children studied, 37.6 % were stunted, 22.8 % were underweight, and 3.9 % were wasted, with 64.3 % experiencing at least one form of malnutrition. Malnutrition was more common among males and children aged 6–12 months. Independent predictors of malnutrition included maternal underweight (BMI <18.5 kg/m2; AOR = 2.87), recent diarrheal disease exposure (AOR = 5.23), and infectious disease exposure (AOR = 2.26). Children of mothers with low education (AOR = 2.37, p < 0.001) and from low-income families (AOR = 2.01, p < 0.001) had higher risk. Exclusive breastfeeding was protective against malnutrition (AOR = 0.39, p = 0.022). Underweight was predicted by maternal underweight (AOR = 2.58, p = 0.004), diarrheal exposure (AOR = 4.34, p < 0.001), and low maternal education (AOR = 2.37, p = 0.002). Stunting was associated with low family income (AOR = 2.01, p = 0.009), maternal underweight (AOR = 2.07, p = 0.006), and exposure to diarrheal (AOR = 2.73, p = 0.001) or infectious diseases (AOR = 3.19, p < 0.001). Wasting was linked to maternal underweight (AOR = 3.13, p = 0.004) and diarrheal exposure (AOR = 4.47, p < 0.001).

The study revealed a high burden of malnutrition among hospitalized under-five children during the COVID-19 pandemic, exceeding national averages for stunting and underweight. Maternal nutrition, education, and child health exposures were key determinants. Interventions should prioritize maternal nutrition, breastfeeding promotion, and prevention of diarrheal and infectious diseases.