|Purpose: Currently the company has increasingly addressed the lack of physical activity and related lifestyle diseases. We know that problems such as obesity or poor posture appeared already in preschool and school-age children, so our paper focuses just on these groups. The aim of the research is to clarify problems of weight training for children and youth. After studying the literature related to strengthening children and young people we found out that Czech literature does not deal with this topic as often as foreign literature. For a long time this issue was neglected. Sometimes lag of knowledge or fear of the negative effects prevents the inclusion of some fitness exercises against little resistance, or exercise using fitness machines in gyms or workout with fitness aids. Methods: Basic guidelines for strengthening children and youth were divided into five age groups with regard to biological age. The paper emphasizes the development of children under the age of 7 years, 8-10 years, 11-13 years, 14-15 years and 16 and older in relation to the strengthening, its specifics and recommendations. Results: If the fundamental principles of the growing body strain is kept and the children and young people work under skilled mentor supervision they are able to train with fitness machines and fitness equipment without any negative effect on them. In addition they improve their posture and power. Conclusion: When creating a training plan, it is important to know how the child movement system develops, mainly how spine developments in every period of ontogenesis. Curvature of the spine develops depending on the back muscles strength. From above mentioned, we conclude the importance of properly strengthening the musculature around the spine at children age and small load on the spine in a vertical direction from the top. Growth cartilages can close step by step and the growth stops prematurely as a result of inadequate physical activity.