The aim of this study was to assess the impact of the COVID-19 pandemic on mental well-being of clinically referred children and adolescents and on their families from the perspective of mental health care professionals in Switzerland during the first year of the pandemic. Psychiatrists and psychologists for children and adolescents participated in an anonymous survey conducted online in April/May 2021. The survey was completed by 454 mental health care professionals, most of them working in outpatient clinics for child and adolescent psychiatry or in independent practices. Most participants indicated an important increase of referrals for depression (86.8% of respondents), anxiety disorders (81.5%), crisis interventions (76.2%), psychosomatic disorders (66.1%), suicidality (63.8%), and behavioral addictions, e.g., excessive gaming (64.6%). In contrast, referrals or treatment demands for disorders such as autism spectrum disorder or psychosis showed no substantial change or a slight decrease, respectively. According to 69% of respondents, patients experienced the highest psychological burden in January/February/March 2021. Family problems very frequently reported by mental health professionals were parents' worries about loneliness/isolation of the child (49%), child's education and academic future (33%), increased media use due to missing options of recreational activities (37.6%), as well as multiple stresses of mothers (36.3%). To conclude, the pandemic has substantially changed the pattern of disorders and the number of clinical referrals of children and adolescents with mental health problems, which has serious consequences for the treatment supply in Switzerland.