The quantity and quality of dietary lipids and their metabolism are of major importance for the growth, body composition, development and long-term health of children, both in health and disease. Lipids are the major source of energy in early childhood and supply essential lipid-soluble vitamins and polyunsaturated fatty acids that are required in relatively high amounts during early growth. Lipids affect the composition of membrane structures, and modulate membrane functions as well as the functional development of the central nervous system. Some long-chain polyunsaturated fatty acids serve as precursors for bioactive lipid mediators, including prostaglandins, thromboxanes and leukotrienes, which are powerful regulators of numerous cell functions such as thrombocyte aggregation, inflammatory reactions and immune functions. Here we review some aspects of the biochemistry and physiology of lipids and their implications for lipoprotein metabolism, energy balance and the lipid supply during early childhood through the placenta, human milk, enteral diets and parenteral lipid emulsions.