Objective To investigate the clinical features, treatment and prognosis of pediatric ANCA-associated vasculitis (AAV) presenting initially with diffuse alveolar hemorrhage syndrome (DAHS). Methods A retrospective analysis was conducted on the clinical data of 6 children, admitted to the hospital from January 2010 to December 2023, who presented with DAHS as the initial manifestation and were eventually diagnosed with AAV. Results Among the 6 children, 4 were female and 2 were male. The median age at DAHS onset was 5.4 ( 4-7.6) years, while the median age at AAV diagnosis was 7.2 (6.3-10.6) years. The interval between DAHS onset and AAV diagnosis ranged from 6 months to 3 years. At the initial diagnosis of DAHS, ANCA testing was negative in all 6 children. All children exhibited varying degrees of anemia and were diagnosed as MPO/p-ANCA-positive microscopic polyangiitis (MPA). Chest imaging primarily showed diffuse pulmonary infiltrations, manifesting as patchy, flocculent, and ground-glass opacities. Hemosiderin-laden macrophages were found in sputum, gastric fluid, bronchoalveolar lavage fluid, or lung biopsy specimens. All 6 children had varying degrees of renal involvement. Treatment for all patients involved glucocorticoids combined with immunosuppressants or biologics. Two children underwent plasma exchange, and one received peritoneal dialysis. During a follow-up period of 24 to 84 months, pulmonary lesions in all 6 children showed significant absorption and reduction compared to previous imaging. No recurrence of hemoptysis or blood-streaked sputum was observed, and symptoms markedly improved. One patient progressed to chronic kidney disease stage 5, receiving regular peritoneal dialysis with stable condition. Conclusions DAHS is a severe complication of AAV. When presenting as the initial manifestation, DAHS may lack other characteristic features of AAV, leading to diagnostic challenges. Clinicians should maintain a high index of suspicion for such presentations. Early definitive diagnosis and aggressive treatment with glucocorticoids combined with immunosuppressants or biologics can effectively improve prognosis.