An effective system of children’s and youth sports, selection and preparation of a the reserve for national teams predetermines the success of athletes in international competitions. Therefore, the development of medical and biological support of children’s sports is an important part of sports medicine. It is proved that when building a training process for different ages, it is necessary to take into account the adaptation processes, as well as the energy supply of the child’s organism. Based on numerous studies, we can conclude that mitochondria play the most important role in the process of energy supply, as well as carnitine, a substance that is a carrier of long chain fatty acids into the cytosol, an activator of beta oxidation and the Krebs cycle. Timely detection of factors adversely affecting and limiting physical activity at the macro level (overtraining, incompatibility of physical activity with the body capabilities) and at the micro level (carnitine deficiency), the ability to eliminate these factors and the adequate use of correction tools help to achieve high results in sports and preserve the health of the athlete.