This article elucidates the emergence of technology-empowered family practices that cross-border families develop to re-spatialize and re-temporalize their family activities and daily rhythms. Standing on the concepts of “doing family” and polymedia, we propose a dual framework of mediated doing/undoing family and explain it in an integrated WeChat environment. Specifically, the frame contains three pairs of dimensions: active versus inactive, everyday co-presence versus absent-presence and invisibility, and historical roots versus anti-traditions. Drawing on a 2-year ethnography of cross-border students communicating with their parents, we use the frame to further illuminate a set of dialectical relations between mediated doing and undoing family, and between cultural motherhood and fatherhood—culturally (un)doing gender. Findings fill gaps in the existing literature on the undoing affordances of technologies, and supplement insights on the experiences of transnational/cross-border parenthood. Our study also discusses the dual dynamics of mediated (un)doing family and presents a critical reflection on the effects of technology on gender asymmetries and gender dynamics.