As smart solutions for healthcare (eHealth) are becoming increasingly widespread, apps and other digital devices may effectively complement various forms of psychotherapy. We point at children and adolescents in psychological therapy as a yet-underserved public for similar solutions. Moreover, a shared design sensibility between interaction designers, game designers, and therapists is still lacking. The Games 4 Therapy initiative was launched to address this problem space through practical design explorations. We illustrate its design research agenda, we call for more attention to children and adolescents as important recipients of digitally-mediated psychological therapies, and we offer actionable concepts and game design tactics for interaction designers and psychotherapists. Finally, we discuss our findings by "thinking through" a selection of conceptual design explorations, pointing at the characteristics and tactics we identified in our sketches.