Advancements in communication technologies and the increasing participation of transnational mothers in digital spaces have attracted growing research interest in ‘motherhood online’. However, limited research has examined how transnational Chinese mothers build supportive communities and negotiate translingual identities while parenting multilingual children in digital contexts. To fill this gap, this study adopts a digital ethnographic and discourse-analytical approach to examine the online interactions of transnational Chinese mothers within a WeChat group in the United States. Informed by the conceptual framework of communities of practice and translanguaging, this study addresses two research questions: (1) How do transnational Chinese mothers engage in translanguaging practices to build a support network in the WeChat group? (2) How do their interactions in the online space reveal the translingual identities of transnational Chinese mothers? Through participant observation of group chat records and follow-up interviews with seven group members, it is found that transnational mothers deploy linguistic and non-linguistic semiotic resources to navigate multicultural contexts, construct a sense of belonging, and represent translingual identities in the digital space. At the nexus of digitally mediated multilingualism, motherhood, and transnationalism, this study brings social, cultural, and educational implications for better supporting transnational families in global mobility.