The surgical treatment of fibrous dysplasia remains a challenge for the pediatric orthopedist because of its high recurrence rate. Although a few successful treatments have been reported by using en bloc resection and bone graft in adults, this has not been reproduced in children. In this report, the authors present two children (2.5 and 6 years old) with monostotic expansile fibrous dysplasia involving the ulna and fibula, respectively, who underwent en bloc resection and autograft to replace the involved bones. Good bone union and functional recovery were obtained postoperatively. However, during a follow-up period of 8 and 5 years, respectively, the lesions recurred completely, and the deformities remained progressing over time. En bloc resection and bone graft cannot prevent recurrence in skeletally immature patients with monostotic expansile fibrous dysplasia, and cannot alter for the natural history of the disease. A combination of other management should be considered in children with fibrous dysplasia.