Comparing, sharing, and shielding children's biological and biographical data in genetic databases and on Facebook are central moves when geneticists and families search for diagnoses for children with rare diseases. Based on ethnographic fieldwork in Denmark, we show that the work of linking children carrying the same genetic mutations forges new sibling-like forms of relatedness between them. With the concept of 'datasociality', we add new layers to 'biosociality' by capturing the ways in which biological information is increasingly mediated by digital and algorithmic processes in the genomic era. In the process of both sharing data and securing anonymity, unrelated children become related through qualities of otherness.