COVID-19; India; Outcomes; Pediatric hematology oncology; antineoplastic agent; bfm 95; bleomycin; cytarabine; dacarbazine; doxorubicin; hydroxychloroquine; hydroxyurea; methotrexate; thymocyte antibody; unclassified drug; vinblastine; adolescent; aplastic crisis; blood transfusion; cancer radiotherapy; chemotherapy; child; clinical article; coronavirus disease 2019; hematologic malignancy; human; Letter; leukemia; male; nasopharyngeal swab; preschool child; retrospective study; reverse transcription polymerase chain reaction; school child; thalassemia major; therapy delay; virus reactivation