Thrombocytopenia is the reduction of platelet number to below normal level. It may be due to the decrease in production, increase in destruction, abnormal spreading in the body or the laboratory errors. B12 deficiency is a rarely seen vitamin deficiency in childhood. It presents with megaloblastic anemia and is difficult to diagnose because of various clinical findings. Here we would like to present two cases which were hospitalized to investigate the etiology of anemia and thrombocytopenia. Cases were detected to have vitamin B12 deficiency which is rarely seen in infantile period. A 12-month old male and a 16-month old female admitted with complaints of weakness, bruise and pallor. On physical examination, there was tremor of upper extremities. Anemia, thrombocytopenia and in peripheral blood macrocytes were detected as laboratory findings. B12 vitamins were found to be low. Patients recovered clinically after parenteral vitamin B12 administration. Laboratory findings also changed into normal.