18F-fluorodeoxyglucose positron emission tomography (FDG-PET) and FDG-PET/computed tomography (CT) are becoming increasingly important imaging tools in the non-invasive evaluation and monitoring of children with known or suspected malignant diseases. In this review, we discuss the preparation of children undergoing PET/CT studies and review radiation dosimetry and its implications for family and caregivers. We review the normal distribution of 18F-fluorodeoxyglucose (FDG) in children, common variations of the normal distribution, and various artifacts that may arise. We show that most tumors in children accumulate and retain FDG, allowing high-quality images of their distribution and pathophysiology.We explore the use of FDG-PET in the study of children with the more common malignancies, such as brain neoplasms and lymphomas, and the less-common tumors, including neuroblastomas, bone and soft-tissue sarcomas, Wilms’ tumors, and hepatoblastomas. For comparison, other PET tracers are included because they have been applied in pediatric oncology. The recent advent of dual-modality PET-computed tomography (PET/CT) imaging systems has added unprecedented diagnostic capability in pediatric oncology by revealing the precise anatomical localization of metabolic information and metabolic characterization of normal and abnormal structures. The use of CT transmission scanning for attenuation correction has shortened the total acquisition time, which is an especially desirable attribute in pediatric imaging.