Objective: We describe qualitative results on facilitators and barriers to participating in a family mindfulness-based intervention (MBI) for youth with ADHD and their parents and perceived effects on child and parent. Method: Sixty-nine families started the 8-week protocolized group-based MBI called “MYmind.” After the MBI, individual semi-structured interviews were conducted with a purposive sample of parents ( n = 20), children ( n = 17, ages 9–16 years), and mindfulness teachers ( n = 3). Interviews were analyzed using Grounded Theory. Results: Facilitators and barriers regarding contextual factors (e.g., time investment), MBI characteristics (e.g., parallel parent–child training), and participant characteristics (e.g., ADHD-symptoms) are described. Perceived effects were heterogeneous: no/adverse effects, awareness/insight, acceptance, emotion regulation/reactivity, cognitive functioning, calmness/relaxation, relational changes, generalization. Conclusion: MYmind can lead to a variety of transferable positively perceived effects beyond child ADHD-symptom decrease. Recommendations on MYmind participant inclusion, program characteristics, mindfulness teachers, and evaluating treatment efficacy are provided.