Digital competence and its different dimensions -- among them responsible online communication -- are competencies that children need to develop for their present and future lives. This article analyzes how teachers promote responsible online communication in Swedish leisure-time centers (LTCs). Based on 20 in-depth interviews, the results show how teachers promote responsible communication mainly in spontaneous situations using mediation strategies such as active mediation, co-use, and participatory learning. The study also identifies educational simulation as mediation strategy. The participants focused primarily on teaching children how not to hurt other people online, as well as issues concerning online safety and privacy. One conclusion is that children's self-selected media use in the LTC provided extended opportunities for promoting responsible online communication.