Climate change and child malnutrition Introductions: Globally, one billion children are living in areas at high risk of climate change exposure. Among them, over 200 million children under the age of five suffer from severe malnutrition, and 148 million experience growth and developmental stunting. Climate change affects key determinants of child health such as the nutritional value of food, environmental conditions, and living standards. Mongolia is classified among countries with a high climate vulnerability index. Therefore, it is essential to study the impact of climate change on children's health in the Mongolian context. We aimed at determining the prevalence and trends of nutritional deficiencies among children under five years of age and to assess the impact of climate change on these deficiencies. Materials and methods: This study was conducted using international databases. Climate change was evaluated using indicators such as the Climate Change Index, average annual land surface temperature, air quality, soil contamination, and precipitation levels. Data on child nutrition were collected from the Institute for Health Metrics and Evaluation (IHME) database and the Mongolian National Statistical Information Service for the period 2000–2019. Nutritional deficiencies were measured using indicators including wasting and overweight among children under five. Trends in the prevalence of nutritional deficiencies were analyzed using the AR(I)MA model to forecast changes between 2020 and 2030. Regional variations were assessed using panel regression models, and the impact of regional climate variables on child nutrition was estimated. Results: The climate vulnerability index in Mongolia has been increasing, with trends indicating further rises in temperature variability. From 2000 to 2019, the prevalence of wasting and stunting among children under five showed a decreasing trend, with annual reductions projected at 0.5% and 1.8%, respectively. In contrast, overweight and obesity among children under five are projected to increase until 2030, with Ulaanbaatar showing statistically significant high values. A correlation was found between climate change indicators and childhood overweight. Conclusions: There is a rising trend in overweight and obesity among young children. Climate change has both direct and indirect impacts on child nutrition, food safety, and nutritional deficiencies. These associations must be taken into serious consideration in public health planning and policy.