This study assesses the bidirectional link between parent-child relationship quality and older parents’ cognitive trajectories over time, with particular attention to potential variations by parents’ gender. Methods: Using a longitudinal, nationally representative sample of parents aged 50 and older from the Health and Retirement Study 2006–2016, the analysis examines three dimensions of the relationship quality between parents and children—contact, support, and strain—in relation to parents’ cognitive function. Parallel latent growth curve models (LGCMs) estimate how baseline relationship quality relates to subsequent change in parents’ cognition and how parents’ baseline cognitive function relates to subsequent change in relationship quality over time. Results: Higher initial levels of relationship strain with children predicts a faster cognitive decline for older parents. Neither initial contact frequency nor initial relationship support is associated with subsequent change in a parent’s cognition, however, good cognitive function predicts a more rapid increase or a slower decline in contact frequency and relationship support over time. No gender difference was found. Conclusion: The results highlight the importance of the “linked lives” of aging parents and their children as well as the potential for bidirectional associations between cognition and family relationships.