The subject of my master's thesis is the relationship between children and the urban environment. The main goal that guided my work was how to improve children's long-term experience of living in an urban environment that is rapidly moving in an unsustainable direction. The starting point for this work was thinking about the question of why children nowadays play less and less outdoors. This was then followed by theoretical research into the wider context of human life in the city, its long-term effects on our health and living environment, the effects of inadequate urban planning on children's lives and habits and reflection on what are the potential solutions to the challenges modern cities face in this regard. All of these was used as input to create a suitable tool - a handbook (activity book) intended for children. The tool purpose is to encourage children in a playful, interesting, and subtle way, to start observing their environment more carefully and to drive them into action and search alternative and creative ways to change things for the better and achieve meaningful interaction with their environment. This master thesis is drawing attention to the importance of involving children in the design of the urban environment. In any case the needs of children and all other social groups must be considered when designing (urban planning, projecting, etc.), but children should be motivated also to design for themselves from an early age and make the most of the circumstances, especially when the first segment fails. With the project I also want to pave the way for my further work in the field of socially responsible design.