Human parents require significant support to raise multiple, highly dependent offspring. Grandmothers are often highlighted as key allomothers (non-maternal caregivers) and their presence is frequently associated with increased child survivorship, leading some to describe humans as cooperative breeders. Equally well documented is the diversity of human childcare systems, where a wide range of individuals support parents including male kin. However, the role of grandfathers has been less well documented, and they seem to have an inconsistent relationship with child survivorship, dependent on socio-ecological factors. Here, we explore the relationship between grandparental allomothering and child survivorship using demographic and time budget data from a pastoralists community in western China. We find that under-five mortality is negatively associated with grandpaternal, but not grandmaternal, living status. Pastoralists in Maqu have recently transitioned from mobile to half-settled livelihoods in which women are more economically active than males. As a result, women's childcare workloads have decreased, while older men (who are excluded from the household economy) supervise children. Our results suggest that patterns of childcare are flexible and highlight the need to consider social and ecological factors to understand allomothering and child survival.