As issues of ethics, criticality, and social impact become more important in computer science, so does the need to teach them in CS classes. Despite the recent growth of academic writing around ethics in CS and a push for teaching ethics in post-secondary CS classes, the K-12 space has largely been ignored. To explore integrating ethics, criticality, and social impact into K-12 CS classes, we interviewed a diverse group of current US K-12 CS teachers to understand how they conceptualize ethics in CS and see potential opportunities and barriers to ethics integration in their classroom context. When asked about ethical issues in CS, many teachers were initially only familiar with cybersecurity and social media. We then presented them with examples of ethical issues relating to three big ideas we identified in the CS ethics literature: algorithmic bias, algorithmic injustice, and techno-solutionism. Finally, we discussed with teachers how they can teach CS ethics in their own classroom context, which surfaced some opportunities and barriers to ethics integration. We end with a discussion of implications for research and practice.