The identification of people with a specific territory (country), with its habitat and attributes has inevitably played an important role in the development of nationality.  Recent social changes have seen a number of psychological theories examining national identities, in-group and out-group favouritism, stereotypes and prejudice development in children.  This thesis attempts to rigorously evaluate these theories in a cross-national study of Scottish and Maltese children aged 5 to 16 years of age.  Study 1 pilots a self-report questionnaire on Scottish children to gauge children’s ability to understand the concept of Nations and National groups, to examine for any in-grouping and out-grouping, and finally to measure any explicit attitude changes with age.  Study 2, carried out in Scotland and Malta, introduces a rating scale task and an interview consisting of open and closed-ended questions to evaluate explicit developmental changes in children’s attitude towards their own nation and a series of out-groups nations.  Study 3 carried out in Malta, develops implicit measures to evaluate differences with internal/external control mechanisms in line with major common theories.  Study 4 carried out in Scotland and Malta, draws upon previous paradigms, uniquely evaluating major theories by using explicit and implicit techniques, quantitatively and qualitatively.  The results demonstrate: 1) that no single theory can fully account for the varying attitude of children in the field of social interactions, at individual and interpersonal process levels; and 2) there is dissociation between explicit and implicit measures for socially sensitive attributes (prejudice); 3) attitudes are not necessarily rigid; 4) gender differences show girls to be less negative than boys; 5) social inclusion has a positive affect on negative attitudes.  The results are discussed in terms of contrasting theories of attitude development.