The sample of K²iD-twins comprises the youngest of altogether four births cohorts of the TwinLife Study. Among these five-year-olds in wave 1 those who did not yet start school were selected for the K²iD-twins study. The project takes advantage of the TwinLife study insofar as rich information about parental behavior and family processes is included, including information about early care. In distinction to the SOEP-ECEC Quality Study where parents received a separate questionnaire as part of the project, measures regarding ECEC attendance, perceived quality of the childcare institution and the address of the current daycare center were included in the main questionnaire for parents as part of the annual TwinLife study. The questionnaire was mostly answered by the mother (90 %). Moreover, other than the SOEP the design is not a household but a family design. Therefore, TwinLife has also information about biological parents who do not live in the same household as the twins.
In a second step, data on the quality of ECEC institutions attended by the twins was collected from directors and group educators of the child’s ECEC institutions. By combining institutional information on the educational context with individual and family data collected in the context of the TwinLife study, this data set allows to examine associations with children’s development during early childhood and school years.