Introduction and objective: The objective of the study was to assess basic immunological parameters in children presenting with seizure disorders during acute infection. Materials and methods: The study was conducted from 19 January 2017 to 5 December 2020 at the Department of Infectious Diseases and Child Neurology in Poznań, and involved 121 patients aged 5–188 months: 64 with febrile seizures and 11 with generalised epilepsy. The control group comprised 46 patients with delayed psychomotor and intellectual development, pervasive developmental disorders, and neurodeficits. A complete blood count with differential white cell count, inflammatory markers, immunoglobulin classes (IgG, IgA, IgM), and the aetiology of infection were analysed using standard laboratory methods in all the cases. Results: Lower IgG was found in the febrile seizures group, and lower IgA was observed in the simple febrile seizure group compared to the patients after epileptic seizures. Patients with first-time simple febrile seizures showed lower IgG levels than the control group. Patients with generalised epilepsy and human herpesvirus 6 (HHV-6) showed lower IgG than the non-infected subjects. Patients with first-time complex febrile seizures had the lowest lymphocyte count compared to the control group. The lowest neutrophil count and total leukocyte count were found in HHV-6-infected patients with simple febrile seizures compared to the non-infected patients. Conclusions: Monitoring basic haematological parameters and immunoglobulin levels is an effective strategy in the diagnosis of seizure disorders in children. Screening tests provide an initial quantitative assessment of humoral and cellular responses, as well as impaired phagocytosis.