The COVID-19 pandemic has significantly impacted the lives of children, youth, and their families and their access to mental health services through new virus containment measures, such as social distancing guidelines, school and service closures, and the emergence of online mental health services. In this study, we utilized a total of 47,417 interRAI assessments to evaluate the impact of the current pandemic on the mental health service needs and referral trends of children and youth across 55 mental health service agencies in Ontario, Canada. Child and youth assessments that were conducted in the period of March 1 to October 31 in 2018 and 2019 were compared with the same period in 2020 to assess pandemic-related differences. Findings demonstrated that mental health assessments among children and youth decreased significantly during the pandemic period, with the greatest decline observed among children from low-income neighborhoods. Results also demonstrated a change in the proportion of mental health concerns previously seen in children and youth. Specifically, referrals for anxiety, depression, self-harm, problem videogaming, and Internet use increased, whereas referrals related hyperactivity/distractibility, risk of harm to others, aggressive, and disruptive behavior decreased. A decrease in bullying and increase in domestic violence exposure was also noted during the pandemic, with no reported differences in children and youth's experiences of physical abuse, sexual abuse, emotional abuse, and neglect. The clinical implications for children, youth, and their families, especially those within more vulnerable communities, are discussed.