Physical activity supports symptom management in children with ADHD and reduces the mental health burden associated with caregiving for children with ADHD. Survey-based research shows that COVID-19 reduced physical activity among diverse populations. This study used a qualitative approach situated within a socioecological framework to (1) understand how COVID-19 impacted physical activity of children with ADHD and their caregivers, to (2) identify barriers to their physical activity, and to (3) identify potential areas of support. Thirty-three participants were interviewed between October 2020 and January 2021. Content analysis revealed that physical activity declined for children and caregivers; significant barriers were social isolation and rising intrapersonal difficulties such as diminishing self-efficacy and energy levels and increased mental health difficulties. Worsening mental health further alienated caregivers and children from physical activity, undermining its protective effects on ADHD symptom management and mental wellbeing. Participants identified needing community support programs that offer virtual, live physical activity classes as well as psycho-emotional support groups. There is vital need to support physical activity opportunities during high-stress situations in families managing ADHD to buffer against diminishing mental wellbeing. This will promote further physical activity engagement and allow families to reap the cognitive, psychological, and emotional benefits.