BACKGROUND: The Sustainable Development Goals (SDGs) prioritize optimal early childhood development (ECD) for all children, emphasizing the principle of leaving no one behind. Despite this focus, the association between disability and ECD remains largely unknown in low- and middle-income countries. This study aims to investigate the impact of disability on ECD among 3 to 4-year-old children in three South Asian countries. METHODS: Data from 56,841 children were analyzed, extracted from six rounds of Multiple Indicator Cluster Surveys conducted in Bangladesh, Nepal, and Pakistan between 2017 and 2020. The outcome variables considered was the early childhood development index (ECDI) and its domains (physical, learning, emotional, and social well-being). Disability status and types of disability considered as the main explanatory variables. The association between explanatory and outcome variables was determined using a multi-level mixed-effect binary logistic regression model, adjusting for potential covariates. RESULTS: Approximately 44% of children in three South Asian countries were not developmentally on track, with prevalence increasing to 58-76% among children with disability. Children with disability exhibited significantly higher odds of not being developmentally on track across all domains compared to those without disability. Country-specific variations were evident, with Nepal consistently showing lower odds than Bangladesh and Pakistan. Likelihoods of poor ECDI and its domains were also observed across types of disability. CONCLUSION: The findings emphasize that children with disability face challenges in achieving developmental milestones, indicating a long-term burden, such as poor education performance and dropout from school. This poses a risk to the achievement of SDGs related to inclusivity and early childhood development. Implementing inclusive education policies, especially in rural areas, and creating supportive environments for individuals with disability are crucial for addressing these challenges.