Childhood malignant melanoma (MM) is extremely uncommon. We report an unusual case of cutaneous melanoma that developed from a medium-sized congenital melanocytic nevus (CMN) in a two-year-old girl. The patient had a history of CMN on the right hip, and she presented with a new ulcerative area with irregular borders and bleeding on CMN. Histopathological examination of the nevus revealed a MM. 18Florfluorodeoxyglucose (18F-FDG) positron emission tomography/computed tomography was performed for metastatic evaluation. The scan demonstrated metastatic increased 18F-FDG uptake in the right external iliac and inguinal lymph nodes.