Respiratory syncytial virus (RSV) is a viral infection that affects the lower airways of infants and young children. With RSV vaccination introduced for infants, identifying characteristics of respiratory vulnerability, including birth weight, is important. This study examined the association between low birth weight and respiratory disease in early childhood, using data from the 2018, 2021, and 2024 Korea National Health and Nutrition Examination Survey. 465 children aged 1–3 years were classified into low birth weight (<2.5 kg) and normal birth weight (≥2.5 kg) groups. The outcome was the presence of respiratory diseases, defined as asthma or allergic rhinitis. Prevalence by birth weight was compared using the Rao–Scott chi-square test, and the association was evaluated using complex sample logistic regression adjusted for age and sex. Among 465 children, 21 (4.6%) had low birth weight and 48 (9.8%) had respiratory diseases. The prevalence of respiratory diseases differed significantly by birth weight (p = 0.0251). Children with low birth weight had higher odds of respiratory diseases (odds ratio [OR], 4.50; 95% confidence interval [CI], 1.26–16.09). Low birth weight was associated with a higher prevalence of respiratory diseases in early childhood. These findings suggest that birth weight may serve as an additional indicator for identifying children at increased risk of respiratory morbidity, supporting early monitoring and preventive care.