The use of theragnostic radiopharmaceuticals in nuclear medicine has grown rapidly over the years to combine the diagnosis and therapy of tumors. In this review, we performed web-based and desktop literature research to investigate and explain the potential role of theragnostic imaging in pediatric oncology. We focused primarily on patients with aggressive malignancies such as neuroblastoma and brain tumors, to select patients with the highest chance of benefit from personalized therapy. Moreover, the most critical and groundbreaking applications of radioimmunotherapy in children's oncology were examined in this peculiar context. Preliminary results showed the potential feasibility of theragnostic imaging and radioimmunotherapy in pediatric oncology. They revealed advantages in the management of the disease, thereby allowing an intra-personal approach and adding new weapons to conventional therapies.