Purpose <p>Malnutrition, anemia, and childhood overweight remain major public health concerns in South America despite economic progress. Understanding their relationship with the Human Development Index (HDI) can inform more effective policy responses. This study examined the association between HDI and maternal and child nutrition indicators across ten South American countries from 2007 to 2021.</p> Methods <p>An ecological study using annual country-level data was conducted for ten countries over 2007–2021. Indicators included childhood anemia, anemia in pregnant women, anemia in women aged 15–49 years, low birth weight, stunting, and childhood overweight. Nutrition data were obtained from the World Bank, and HDI values from the UNDP. All variables were standardized (z-scores) and analyzed using simple linear regression with robust standard errors clustered by country. Non-linear associations were explored using natural cubic spline models.</p> Results <p>Childhood anemia decreased substantially in Bolivia, Peru, Brazil, and Ecuador, while stunting declined in Ecuador, Paraguay, Bolivia, and Peru. Childhood overweight increased in Argentina, Paraguay, and Uruguay. Higher HDI was significantly associated with lower prevalences of childhood anemia, maternal anemia, anemia in reproductive-age women, low birth weight, and stunting. Conversely, HDI was positively associated with childhood overweight. Spline models identified significant non-linear components for anemia indicators and stunting, with partial non-linearity for low birth weight and overweight.</p> Conclusions <p>Higher human development in South America is associated with reductions in anemia and stunting but with increases in childhood overweight, reflecting a regional nutrition transition. Policies must sustain progress in undernutrition reduction while implementing early strategies to prevent childhood obesity.</p>