One of the public health measures to contain the Sars-CoV-2 outbreak and with major impact at national and international level was the closure of schools. It is believed that school closures are effective in forcing parents to work from home, thereby severely limiting work-related contacts, and in significantly reducing children's activities and contacts. However, school closures have a significant impact - for example, they can lead to economic damage to parents through the need for parental childcare. The transfer of childcare responsibilities to at-risk grandparents, as well as the loss of education in socially disadvantaged families and social isolation of children, can also have far-reaching consequences. There is no data available on the implementation of school-based social distance measures during the corona pandemic or any other epidemic that has occurred in recent years. It is therefore far from clear how effective school closures are compared to other social distance measures and how much they contribute to transmission control. Another question that arises in this context is what the percentage of children in Switzerland who have undergone SARS-CoV-2 infection is. International research results show that the percentage is very low, ranging from 1% for small children to 6% for older children (http://www.corona-data.ch/). These figures do not give any indication of the actual seroprevalence (rate of infection) of SARS-CoV-2, as the tests were restricted to risk groups and persons with symptoms. Furthermore, the indications for the tests were not uniform and were handled heterogeneously. It is therefore not known whether children are less frequently infected or simply less symptomatic. Even though children and adolescents are less likely to develop severe SARS-CoV-2 than adults, there may be severe courses with immunological shock and even deaths. Knowledge about 1. the population-related seroprevalence of SARS-CoV-2 in young people, 2. the transmission routes from and among children and adolescents and teachers in schools, 3. the asymptomatic infection rate in adolescents, 4. the chance of long-term immunity or reinfection (in children and adults) and 5. the influence of school opening and protective measures on the temporal spread of the virus in children is almost completely lacking. Knowledge from a population-based cohort of children and adolescents in schools over time would help to answer these critical questions. The results would inform policy-makers on how young people should be treated during the pandemic, especially in schools, but also on the severity of social distancing measures towards their parents and grandparents.