Background: Few data exists on paediatric neuromyelitis optica spectrum disorder (NMOSD). Here, we investigated the clinical presentation, treatment responses and long-term prognoses in a large cohort of patients with NMOSD and compared between children and adults with aquaporin-4 antibody (AQP4-IgG). Methods: A retrospective chart review of patients followed in multiple centres identified 127 patients with NMOSD (31 children; 96 adults). Data were collected through medical records and structured questionnaire. Results: In the paediatric cohort, median age at onset was 14 (range 7–17) years; 87% were female. AQP4 and myelin oligodendrocyte glycoprotein antibodies were detected in 82% and 16%, respectively. During a median disease duration of 48 months, 23% developed visual acuity of <6/60 Snellen, 3% were wheelchair-dependent. The frequency of brain/brainstem phenotype (18% vs 9%, p = 0.018) was more common in AQP4-IgG-positive children, while AQP4-IgG-positive adults were more likely to present transverse myelitis (TM) (44% vs 29%, p = 0.005) of all 452 episodes. Multivariable analyses showed that sustained disability was independently associated with the presence of TM (p = 0.030), brain/brainstem symptoms (p = 0.010), annualized relapse rate (p < 0.001) and possibly age of onset (p = 0.069). The reduction of ARR after azathioprine was more prominent in adults (79%) than in children (48%). Mycophenolate mofetil and rituximab decreased the relapse frequency of children, with a reduction of 94% and 100%, respectively. Conclusions: paediatric NMOSD is a severely disabling disorder characterized by repeated brain attacks and early disability accrual. Prompt therapy including mycophenolate mofetil and rituximab should be considered to improve paediatric care.