The coronavirus disease 2019 (COVID-19) pandemic is profoundly affecting human life around the world. While the mental health of patients and quarantined is of increasing concern, the general public’s mental health also requires significant attention. COVID-19 also has the potential to threaten the mental health of children and adolescents significantly. This paper reviews the effects of the pandemic on the mental health of the general public, including children and adolescents. The risk factors for mental health problems are also reviewed. South Korea has implemented preemptive and aggressive quarantine measures against COVID-19. Mental health professionals have performed various psychological services to support the general public immediately and actively. This paper presents those supporting measures and discusses their limitations. Recognizing the importance of the impact of the pandemic on the mental health of the general public, observing its direct and indirect consequences, and organizing a multi-disciplinary system based on empathy and collaboration are important for developing effective support measures. In particular, national policies and support are needed to implement them.