<p>Early-onset vitamin B₁₂ deficiency is an important but often overlooked cause of anemia and neurodevelopmental delay in infants. We retrospectively reviewed seven exclusively breastfed infants (4 males, 3 females; age 3.5–18 months), of vegetarian mothers, presenting with symptomatic B₁₂ deficiency across four hospitals in North India. All infants demonstrated anemia and cutaneous hyperpigmentation. Neurological findings ranged from irritability and subtle motor delay to gross hypotonia, developmental regression, tremors and seizures. One infant had low normal vitamin B₁₂ levels and remaining six infants were deficient. Amongst the mothers, three mothers were deficient in serum B₁₂ and remaining four had B₁₂ levels in low normal range. In those infants and mothers in which serum B₁₂ was in low normal range, serum methylmalonic acid (MMA) was markedly elevated, highlighting the functional deficiency of vitamin B₁₂. Parenteral B₁₂ therapy led to rapid hematologic recovery and neurological recovery on follow-up. This case series highlights exclusively breastfed infants of vegetarian mothers as a high-risk group for vitamin B₁₂ deficiency and underscores the importance of early recognition and functional testing to prevent irreversible neurological sequelae.</p>