Infections around the hip and the pelvic girdle mimicking septic hip arthritis are rare conditions in the pediatric population requiring urgent treatment. They are not readily diagnosed because of rarity, resemblance to septic hip, and unclear pathophysiology, which often results in misdiagnosis, delayed diagnosis, and delayed treatment. The aim of this study was to prove the key role of magnetic resonance imaging (MRI) as the first-line modality in making a early definite diagnosis of an uncommon perihip infection in children. We retrospectively reviewed 20 children with a provisional diagnosis of unilateral septic hip who were confirmed finally to have perihip infections and combined with concomitant osteomyeltis using MRI. All patients were treated with intravenous antibiotics with or without abscess aspiration until normalization of clinical symptoms and laboratory tests including serum C-reactive protein and erythrocyte sedimentation rate. All infections healed successfully and the final C-reactive protein was recovered to a mean of 0.37 mg/dl (range 0.01–0.78 mg/dl) without recurrence or complication. Although the MRI is costly and limited in practical application, it was found to be effective as a primary diagnostic tool for an early, accurate diagnosis of infections around the hip and the pelvic girdle in children to correctly guide the decision and the approach for treatment.