Despite the SARS-CoV-2 virus being present worldwide, and although it is now clear thatchildren are affected by the disease with milder symptoms than adults, many immunologicalquestions, which are very relevant for Public Health reasons and for the organization ofservices, remain unsolved. The role of serology for the diagnosis of COVID-19,particularly in the pediatric age, is still very uncertain. Preliminary evidence suggeststhat not all children with SARS-Cov-2 infection develop antibody levels that can bedetected by currently employed methods. This makes it crucial to identify othermethodologies that are able to evaluate the true prevalence of prior SARS-CoV-2 infectionin the pediatric population. Many other aspects of the immunological mechanisms ofresponse to SARS-CoV-2 are also uncertain, such as the role of cellular immunity, andgenerally the role of immunity (cellular and antibody) in protecting against the diseasein the medium and long term. Finally, questions remain open regarding cross-immunity withother previously circulating coronaviruses and their impact on the pediatric populationin terms of protection against COVID-19 infection, disease development, or reinfection.This study aims to help clarify the role of serology and other immune response tests inthe diagnosis of COVID-19 in the pediatric population. Specifically, it aims to assess:the prevalence of SARS-CoV-2 seroconversion cases among the pediatric populationaccessing the National Health System (NHS), at different moments in time and in differentregions of Italy; whether cellular immunity tests can help to identify children who havehad SARS-CoV-2 infection, particularly children with low antibody levels, and thus tobetter estimate the prevalence of prior SARS-CoV-2 infection; the prevalence ofcross-reactivity with other coronaviruses; whether immunity (antibody and cellular) isprotective in the medium/long term; and if there are healthy carriers, i.e. individualswho have had prior SARS-CoV-2 infection, who are asymptomatic but may harbor SARS-CoV-2in the pharynx, with the risk of transmitting it.