The exchange of informal support within the social network plays a vital role in enabling older adults to remain living in the community as they age. Following spousal loss in later life, the exchange of instrumental support is of particular importance in order to meet the practical and financial needs of the bereaved spouse. Adult children are typically the primary source of social contact and informal support for older widowed adults following bereavement. However, very little is known of the longitudinal changes that occur in the exchange of instrumental support with children during the transition to late-life widowhood. Trajectories and predictors of change in material and time support exchange in parent-child relationships were modelled over a 15-year period for 1,266 older adults (mean age 76.7 years). Widowed older adults received more material and time support from their children than their married peers. Proximity to children, age at spousal loss, self-rated health, cognitive functioning and income were predictive of levels of exchanged instrumental support in late-life widowhood. Short-term reciprocity appears to continue in parent-child relationships during late-life widowhood. The implications of the findings for policy and practice are discussed, including the role of children in the support networks of older widowed adults and the potential difficulties faced by those who do not have access to informal avenues of support.