Under-nutrition and obesity are multi-determined. The multiple determinants of either under-nutrition or obesity are linked, thus forming a system of influences. How a system of linked multiple influences functions is illustrated with specific reference to early nutritional deficiencies. The traditional explanation that child nutritional deficiencies are due to food scarcity or a lack of family economic resources has been increasingly questioned. In the UNICEF extended care model, deficiencies in children's nutritional intake are due to family economic and food resources and to specific caregiver resources. The role of three caregiver resources, maternal education, intelligence and depression are reviewed. Evidence also is presented on the need to take into account child characteristics, as an additional set of influences on nutritional deficiencies. Using a systems perspective this review documents how the relation to nutrition of family and caregiver resources and child characteristics can be mediated or moderated by alternative linked influences such as cultural characteristics, maternal input into family economic decisions and social support networks. Based on this review a revised extended care model is presented, explicitly integrating child characteristics and specific mediating and moderating links between multiple predictors of child nutritional deficiencies. This is followed by a brief discussion on how a systems perspective can also apply to the study of childhood obesity.