Background: Children living in conflict zones experience high levels of psychological distress. Schools can provide an accessible setting for support, yet evidence on the effectiveness of school-based interventions in active war contexts remains limited. Objectives: To evaluate children’s well-being and internal coping resources during the war in Ukraine and to examine the feasibility of a school-based program designed to enhance psychological well-being in preadolescents. Participants and setting: The study involved 81 children aged 10–12 years from schools in Lviv, Ukraine. Methods: Adverse Childhood Experiences (ACEs), PTSD symptoms, quality of life, self-compassion, and mindfulness traits were assessed using standard questionnaires and validated psychometric scales. The intervention program, delivered at school, focused on mindfulness, self-compassion, social connection, sense of purpose, and trauma processing. Acceptability and perceived impact were evaluated post-intervention among children, families, and school staff. Results: 42% of children reported four or more ACEs. 39.5% of children exceeded the clinical cutoff for probable PTSD on the CRIES-8 scale, with differences observed between boys and girls. Higher levels of self-compassion and mindfulness were associated with lower PTSD symptoms. Children, families, and school staff reported improvements in children’s well-being, emotion regulation, and social functioning after the intervention. Conclusions: Self-compassion and mindfulness training may serve as protective factors against PTSD. Our findings provide encouraging preliminary evidence supporting the potential of a school-based intervention to promote children’s psychological well-being in an ongoing war setting. Future studies with larger samples, control groups, and objective measures will help strengthen the generalizability of these findings.