Childhood and adolescence are decisive periods in human life. Body composition and psychological changes determine nutritional requirements as well as eating and physical activity behavior variability. Aims of the present paper are to discuss recent advances in measurements for quantifying total body and regional adiposity, and for mapping adipose tissue distribution in order to evaluate metabolic risk factors in children. Among the new methods available for assessing pediatric body composition, magnetic resonance imaging (MRI) can serve as a reference method for measuring tissue and organ volumes because estimates is reliable independent of age. MRI is the method of choice for calibrating field methods designed to measure adipose tissue and skeletal muscle in vivo and is the only method available for measurement of internal tissues and organs. MRI can be used to validate measures of important molecular level components such as fat measured by dual energy X-ray absorptiometry and bioimpedance analysis. Moreover, the large gap in available information for certain topics makes MRI measurement a dynamic and growing scientific area of body composition investigation.