Objectives Across cultures, fosterage has been shown to impact child health. Contextual factors, such as the reason for fosterage and the relationship between foster parent and child, are known to magnify variance in nutritional outcomes for foster children. Another important, but less studied, factor is the role of gender. Sex‐biases in physiology and cultural norms are both known to affect child nutrition, and we posit these effects might be magnified in the presence of fosterage. In this study, we investigate how sex interacts with fosterage to affect nutritional outcomes among Namibian pastoralists. Methods Anthropometrics for children and adults were collected using standard procedures, and linear models were used to predict the effects of age, sex, and fosterage on height, weight, and body mass index Z‐scores. Semi‐structured interviews with adults provided context for understanding sex specific reasons for fosterage and biases in investment. Results Boys in this population have lower nutritional scores than girls, and fostered boys have lower weight and BMI Z‐scores than nonfostered boys. Fostered girls have lower height Z‐scores and are more likely to be stunted and underweight than nonfostered girls. These effects extend into adulthood, with fostered women being shorter than their nonfostered counterparts. Conclusions Sex plays a role in the nutritional impact of fosterage among Himba children. These differences could be related to differential child labor demands, investment patterns, and the divergent reasons girls and boys are placed into fosterage. Future studies should consider how fosterage can magnify existing biases, like sex, when studying its impact on child health.