Differentiated thyroid cancer (DTC) is rare in the pediatric population. It remains unclear whether younger children are at greater risk of more aggressive disease. We aimed to identify prognostic factors for aggressive pediatric DTC and to define an appropriate age stratification. This retrospective cohort study included all patients aged 18 years or less who were treated for DTC between 1985 and 2021 in a tertiary medical center and were followed up for a minimum of 1.5 years after treatment. Seventy-eight patients were included, all diagnosed with papillary thyroid carcinoma: 30 (38.5%) low-risk, 21 (26.9%) intermediate-risk, and 27 (34.6%) high-risk according to the American Thyroid Association (ATA) risk stratification. The mean duration of follow-up was 11.8 ± 7.8 years. No evidence of disease was documented in 52 patients (66.7%) at 1-year post-treatment and 64 patients (82.1%) at the end of follow-up. On analysis by age, evidence of disease at 1-year post-treatment was found in 66.7% of children younger than 11 years, compared to 25.4% of older children (p = 0.002). There was no significant difference by age in evidence of disease at the last follow-up (p = 0.453). Patients aged <11 years at diagnosis were associated with more aggressive disease features on histopathologic examination, metastatic disease, and high ATA risk level. Patients aged <8 years were associated with more frequent bilateral disease and extrathyroidal extension. Pediatric DTC patients who are younger than 11 years at diagnosis have more aggressive disease features and a lower early remission rate than older patients. Nevertheless, their long-term outcome is satisfactory. 4-retrospective cohort study Laryngoscope, 134:4818-4825, 2024.