Background To explore the characteristics and regularity of complete blood count (CBC) changes among influenza A-positive child patients and to discover parameters that can help with the diagnosis and differential diagnosis. Methods One hundred and ninety-one influenza A-positive children, two hundred and nineteen influenza A-negative children with influenza-like symptoms, and two hundred and forty-seven healthy children were included in this study. They were divided into three groups: influenza A-positive patient group, influenza A-negative patient group, and control group. Reverse transcriptase polymerase chain reaction testing and Sysmex XS-800i hematology analyzer were used to obtain influenza A and CBC results, respectively. CBC along with parameters including lymphocyte-to-monocyte ratio (LMR), neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), mean platelet volume/platelet ratio (MPV/PLT), and lymphocyte*platelet (LYM*PLT) was calculated and recorded for each child. The differences in these parameters among different groups were tested with SPSS 15.0. The diagnostic values were also evaluated. Results The LYM and PLT of child patients with influenza A were significantly lower than those of both influenza A-negative patients with influenza-like symptoms and healthy controls. Among all the parameters, LYM*PLT has the largest area under the curve and the highest diagnostic value, followed by MPV/PLT. Compared with using LMR or MPV/PLT, the diagnostic value of using LYM alone was, on the contrary, higher. Conclusions Low LYM*PLT and high MPV/PLT may indicate influenza A infection in children with influenza-like symptoms, which can be a useful indicator for diagnosis and differentiation of influenza A infection.