This correlational study investigates the relationship between mobile phone use among elementary school students in Iran during the COVID-19 epidemic, and its effect on emotional-behavioural functioning and academic and social competencies. A researcher-devised questionnaire, and the Achenbach Child Behaviour Checklist (CBCL)-parental version, was used to assess parental perception of the effects of mobile phone use. Questionnaires were completed by 500 parents, of which 470 were analysed. Findings showed a perceived relationship between the use of cyberspace (smartphone, tablet, games, and social networks) and anxious/depressed, withdrawn, somatic complaints, social problems, thought problems, attention problems, antisocial behaviour, and aggressive behaviour in children. Findings indicate that children's cultural context affects their exposure to online dangers, including receiving threatening images and messages, and cyberbullying; the effects in the current study being lower than the international average. It is recommended that there should be focus on promoting students' media literacy, and parental awareness.