Background: All femoral or tibial fractures regardless of associated injuries, intramedullary nailing (IMN) has its more advantages in rapid rehabilitation, good effects on the child and his family and strong fixation. Objective: To assess the role of elastic stable IMN in union of diaphyseal fractures of long bones in children. Patients and Methods: A prospective and retrospective analytical study on ten children with isolated femoral or tibial fractures who were admitted to Orthopedic Department, Zagazig University Hospitals. They were divided equally into group I that included 5 patients with femoral shaft fracture managed with IMN and group II, which included 5 patients with tibial shaft fracture managed with IMN. Their mean age was 4.7 years old. Results: When the groups compared, the spica cast group was found to have a shorter duration of hospital stay compared to elastic nail group. The knee range of motion of the spica cast group was found to be better compared to the elastic nailing group. The elastic nailing group was found to have started walking earlier both with and without support. Patients with intramedullary nailing started to walk with aid after one month and independently after 2 weeks. Patients with spica cast started to walk with aid after 2 months and independently after 12 weeks. Conclusion: None of the available treatment tools to fix diaphyseal long bones fractures in preschool children is perfect because each method has its own set of complications. However, constitute the motive for developing new techniques or changing the design of currently available devices.