Sexing the skeletal remains of young individuals is crucial yet notoriously difficult in archaeology. Children, who cannot be reliably sexed morphologically, are often excluded from gender-related research, limiting our understanding of past childhood. This issue is compounded in contexts lacking grave goods, such as early Christian burials. We conducted genomic screening of 142 individuals from Sweden dating from the late Viking Age to the Medieval period, including 68 subadults and 74 adults from 27 single and 50 multiple burials. To investigate the treatment of children in death and the role of collective graves, we applied genomic sexing and kinship analyses to individuals from three sites. Contrary to the assumption that collective burials reflect close kinship, our results show that children interred with adults rarely shared close biological ties. Burial patterns indicate that gender roles were established early, with both boys and most girls mirroring adult spatial patterns. However, flexibility existed, and extended kinship likely played a central role in structuring these communities.