Thrombocytopenia in six-month-old babies may be caused by primary thrombocytopenia, other hematologic disorders, hypersplenism and other causes. 1. Primary thrombocytopenia: many six-month-old babies with thrombocytopenia is an immune disease, the presence of anti-platelet antibodies in the blood circulation, normal platelets are destroyed, which will cause thrombocytopenia. 2. Other blood system diseases: thrombocytopenia in six-month-old babies may be caused by blood system diseases, such as leukemia, aplastic anemia, infections inhibit the hematopoietic function of the bone marrow, thus causing insufficient platelet production and thrombocytopenia. 3. Hypersplenism: six-month-old babies have enlarged spleen or hypersplenism due to various reasons, which causes excessive retention of platelets in the spleen, and the number of platelets in the blood decreases accordingly. The causes of thrombocytopenia in six-month-old babies are more varied, and the specific ones can only be determined by going to the hospital and going through the examination.