PLG and COVID-19: We found that a considerable number of biological processes and metabolic pathways enriched in COVID-19-children against COVID-19-adults or healthy children were overlapped, such as platelet degranulation (GO:0002576), blood coagulation (GO:0007596), fibrinolysis (GO:0042730) and plasminogen activation (GO:0031639) in the proteomic level (Figure 2E), and ABC transporters (KEGG ID: map02010), biosynthesis of amino acids (KEGG ID: map01230) and pyrimidine metabolism (KEGG ID: map00240) in the metabolic level (Figure 2F).