A two-month-old baby boy on prophylaxis anti-tuberculosis (anti-TB) since the age of two weeks presented with several episodes of seizures. He was afebrile and metaphyseal widening of both lower and upper limbs were noted on clinical examination. Laboratory investigations revealed hypocalcaemia, elevated alkaline phosphatase (ALP) and vitamin D deficiency. This case report discusses the possible causes of vitamin D deficiency in a child and highlights that although exclusive breastfeeding and limited sun exposure are the main cause of vitamin D deficiency, other risk factors need to be considered.