Background: During the coronavirus disease 2019 (COVID-19) pandemic, children and families have had to adapt their daily lives. The purpose of this study was to describe changes in the weight-related behaviors of children with obesity after the onset of the COVID-19 pandemic. Methods: Semistructured interviews (n = 51) were conducted from April to June 2020 with parents of children with obesity. Families were participants in a randomized trial testing a clinic-community pediatric obesity treatment model. During interviews, families described their experience during the COVID-19 pandemic, with a particular emphasis on children's diet, physical activity, sleep, and screen time behaviors. Rapid qualitative analysis methods were used to identify themes around changes in children's weight-related behaviors. Results: The mean child age was 9.7 (±2.8) years and the majority of children were Black (46%) or Hispanic (39%) and from low-income families (62%). Most parent participants were mothers (88%). There were differences in the perceived physical activity level of children, with some parents attributing increases in activity or maintenance of activity level to increased outdoor time, whereas others reported a decline due to lack of outdoor time, school, and structured activities. Key dietary changes included increased snacking and more meals prepared and consumed at home. There was a shift in sleep schedules with children going to bed and waking up later and an increase in leisure-based screen time. Parents played a role in promoting activity and managing children's screen time. Conclusions: The COVID-19 pandemic has created unique lifestyle challenges and opportunities for lifestyle modification. Clinical Trials ID: NCT03339440.