Children and childcare workers (CCWs) from day care centers (DCCs) were allocated (per DCC) to 1 of 4 surveillance modules, with respiratory sampling (laboratory analysis by polymerase chain reaction) planned for a period of 12 weeks. Blood sampling (finger prick test) for seroprevalence was conducted before and after the sampling period. Respiratory sampling was accompanied by psychosocial questionnaires at weeks 1, 6, and 12, and qualitative interviews were performed for a representative subsample of participants. As an additional service outside the regular testing schedule, on-demand testing was offered also for symptomatic DCC children and CCWs from modules 1, 2, and 3.