Mindful Gnats is a computer game and App that introduces mindfulness and relaxation skills to young people aged nine years and older. In this paper the authors describe their model for using technology to support children with the development of psychological skills. This model combines a computer game to introduce and practice psychological skills played in the presence of an adult, with an App that assists young people as they practise and transfer those skills into their everyday life at home, at school and in the community. The Mindful Gnats computer game comprises a six level 3-D game world and is available on iOS and Windows. The Mindful Gnats App is available for both iOS and Android operating systems. This paper describes the background research that informed the design of Mindful Gnats as well as the specific mindfulness and relaxation contents of the programme. The authors' on-going research to evaluate the effectiveness of Mindful Gnats with regular children and those with clinical difficulties is described, along with the key lessons the authors have learnt from their experience in the design of mental health promoting technology.