BACKGROUND: Blood cancer is the most common type of cancer and the leading cause of death by disease past infancy among children. Children with blood cancer are vulnerable population to viral infections such as coronavirus disease 2019 (COVID-19). OBJECTIVES: To estimate the incidence of COVID-19 in children with blood cancer and analyse the demographic parameters, clinical characteristics and treatment outcomes in children with blood cancer with COVID-19 illness. METHODS: We adhered to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline and searched ProQuest, Medline, Embase, PubMed, CINAHL, Wiley online library, Scopus and Nature for studies on the development of COVID-19 in children with blood cancer, published from December 1, 2019 to April 30, 2023, with English language restriction. RESULTS: Of the 3077 papers that were identified, 155 articles were included in the systematic review (83 case report, 54 cohort and 18 case-series studies). Studies involving 1289 children with blood cancer with confirmed COVID-19 were analysed. Leukaemias (1141 cases) were the most frequent types of blood cancer observed in children who developed COVID-19, followed by non-Hodgkin's lymphomas (59 cases), Hodgkin's lymphomas (36 cases), Langerhans cell histiocytosis (7 cases), myelodysplastic syndrome (7 cases) and myeloid neoplasm (1 case). Among all 1289 blood cancer paediatric cases who transmitted severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), some children were documented to be admitted to the intensive care unit (ICU) (n = 175, 13.6%), intubated and placed on mechanical ventilation (MV) (n = 111, 8.6%), suffered acute respiratory distress syndrome (ARDS) (n = 144, 11.2%) or died (n = 111, 8.6%). Overall, COVID-19 in children with different types of blood cancer resulted in no or low severity of disease in 78.6% of all included cases (COVID-19 severity: asymptomatic = 238, mild = 601, or moderate = 171). Treatment for COVID-19 was not necessary in a small number of children with blood cancer (n = 94, 7.3%). Fatality in children with blood cancer with COVID-19 was reported in any of the included blood cancer categories for leukaemias (n = 99/1141, 8.7%), non-Hodgkin's lymphomas (n = 7/59, 11.9%), Hodgkin's lymphomas (n = 2/36, 5.5%), myelodysplastic syndrome (n = 1/7, 14.3%) or myeloid neoplasm (n = 1/1, 100%). Fatality rate in children with blood cancer infected with SARS-CoV-2 was the highest in patients with Hispanic ethnicity (n = 44/111, 39.6%) and COVID-19-related fatality was highest in male patients (76.5% of deceased patients). Most studies reported to alter the intensity and regimen of anticancer treatment in children with blood cancer during course of SARS-CoV-2 infection, however, many studies have reported to successfully treat COVID-19 without any changes to the anticancer treatment. CONCLUSION: Globally, leukaemias were the most prevalent and myeloid neoplasms were the least prevalent blood cancer types in children who developed SARS-CoV-2 infection. Children with blood cancer infected with SARS-CoV-2 may experience higher rates of ICU admission and mortality in comparison with the healthy pediatric populations. Mortality in children with blood cancer and infected with SARS-CoV-2 was highest in cases belonging to male gender and Hispanic ethnicity. However, children with blood cancer tend to have milder COVID-19 symptoms and are less likely to be hospitalized and have better prognosis when compared to adults. Continuation of anticancer treatment in individual paediatric blood cancer patients with COVID-19 seems to be possible.