PIP: A microeconomic model of the process by which infants and preschoolers are subject to malnourishment, diarrhea and other illnesses in developing countries is given. The model is econometrically based of a cross-section time-series for 1200 children from Candelaria, Colombia. Four primary issues are addressed: economic constraints and intra-family resource allocation decisions impacting on a child's nutritional and health status; the interrelationship between malnutrition, diarrhea, and other diseases; specific policy interventions (maternal-child health education, food supplementation and the encouragement of breast feeding) impacting on health and nutritional status; and the need to distinguish between the effect of different policy variables on a child's height and weight during infancy and preschool age. The observations were taken over a 7 year period during the Promotora maternal-child health program in Colombia.