Introduction - The effectiveness of closing daycare centers and schools in controlling the SARS-CoV-2 epidemic is unknown, particularly because the role of children in transmission chains has not been fully established. Materials and Methods - From May 29 to July 2, 2020, a retrospective study tracked the circulation of the virus during the lockdown period in two populations: hospital healthcare workers in Seine-Saint-Denis who were called upon to care for COVID-19 patients, and early childhood professionals who were called upon to work in hospital daycare centers caring for the children of the former. A questionnaire documented participants’ symptom history, contacts with suspected or confirmed COVID-19 cases, and sociodemographic characteristics. A blood sample was tested for anti-SARS-CoV-2 antibodies. Results - The attack rate was 11.5% in the hospital healthcare worker population (6/52) and 17.4% among daycare workers (8/46). An early outbreak occurred among staff at the Montreuil daycare center: it did not affect the parents of the children in care during that period (p=0.029). In Aulnay-sous-Bois, 3 daycare workers were infected: none had cared for the child of an HIV-positive healthcare worker; similarly, among the parents of children who had been in the care of these 3 workers, none developed antibodies. Twelve of the 14 infections could be linked to a probable source of infection, most often a colleague. Discussion-Conclusion - The reconstruction of viral transmission between the two populations in our study suggests that the children cared for in these two daycare centers did not contribute to the spread of the virus.