Understanding the circumstances in which children migrate is important to ensure their well-being. Yet, child migration in sub-Saharan Africa is not easy to measure. Health and Demographic Surveillance Systems (HDSS) provide an excellent opportunity to estimate child migration in the region. I examine out-migration patterns of children younger than 15 in eastern and southern Africa, where adult mortality is high, fostering is prevalent, and households are dynamic. Using longitudinal data pooled from 15 HDSS, covering roughly 451,000 children, I find that most children who migrate do so with their mothers (tied migration). Moreover, an intergenerational link between a mother's and her child's mobility is evident: children whose mothers are migrants are more likely to migrate themselves. Despite some expectations of agency in child mobility in later childhood (for education or work), children who out-migrate independently of their mothers are often orphaned or have mothers living elsewhere. Maternal death is a forceful driver of child migration, especially within six months following a mother's death. Thus, orphaned migrants are exposed to the double shock of losing a parent and a change in their immediate environment. However, children in larger households tend to migrate less, somewhat dampening the mobility of orphans.