Background and Clinical Significance: Vitamin B12 deficiency in infancy is an uncommon but reversible cause of severe hematologic abnormalities and potential neurologic injury, particularly in exclusively breastfed infants whose vitamin B12 status depends on maternal stores. Because its clinical presentation may mimic bone marrow failure syndromes or hematologic malignancies, diagnosis can be challenging and delayed; Case Presentation: We report a case of early infantile pancytopenia ultimately attributed to profound vitamin B12 deficiency secondary to maternal celiac disease. Prompt recognition and treatment with cobalamin supplementation resulted in rapid hematologic recovery and a favorable clinical outcome; Conclusions: This case underscores the importance of considering vitamin B12 deficiency in the differential diagnosis of unexplained cytopenias in infants and highlights the critical role of maternal nutritional status in neonatal health. Improved awareness and targeted screening of at-risk mothers during pregnancy and lactation may prevent severe but readily treatable complications in affected infants.