This paper investigates the association between thermal stress and child health outcomes in India by linking individual-level data from the National Family Health Survey (2019–21) with high-resolution climate reanalysis data. The study examines the effects of multiple thermal indicators, 2 m temperature, mean radiant temperature, and Universal Thermal Climate Index on stunting, wasting, underweight, and concurrent stunting and wasting among children under five. Logistic regression models adjusted for socioeconomic and maternal characteristics indicate that the likelihood of acute undernutrition (wasting and underweight) increases significantly with higher heat exposure, particularly among socioeconomically disadvantaged households, whereas stunting levels decrease. The analysis identifies heterogeneity by sex, residence, maternal education, and access to electricity. The findings underscore the role of heat stress as a determinant of acute child malnutrition, particularly in socioeconomically disadvantaged populations. Integrating climate information into public health and nutrition programs is critical to safeguarding child growth and resilience in a warming climate.