Many voluntary associations during the interwar years promoted international understanding in the hope of avoiding another global war. The League of Nations Unions in Britain lobbied the government to advocate for the newly founded League of Nations, whilst also seeking to convince and educate a wider public, promoting a ‘world citizenship’ that crossed national boundaries. Children and young people were a key constituency for the LNU’s promotional efforts as they would be the ones to take its agenda forward in the future. To create world citizenship among this younger generation, the LNU argued that ‘new knowledge’ alone was insufficient; a ‘change of feeling and purpose’ was also required. This article focuses on the ‘change of feeling and purpose’, the emotional terrain of the LNU’s vision of world citizenship, with an emphasis on international friendship, hope and fear. Drawing on selected exemplars from the LNU’s Education Committee publications, school magazines, and memoirs and oral histories, it explores ways in this emotional terrain was envisaged by adults in the LNU, and was experienced and articulated by young people themselves.