We studied the psychosocial impact of the start of the COVID-19 pandemic on Dutch children with cancer in outpatient care and their caregivers (n = 799) using regular monitoring and screening outcomes. No differences were observed between the pre-COVID-19 and early-COVID-19 periods in health-related quality of life and fatigue of children. Fewer caregivers were distressed during the COVID-19 period than pre-COVID-19. In conclusion, the additional stress of COVID-19 did not deteriorate psychosocial functioning of children with cancer and their caregivers. Results may be explained by alleviating daily life changes, experience in coping with medical traumatic stress, and appropriate care and support.