IntroductionUnited Nations (UN) agencies are influential global health actors that can introduce legal instruments to call on Member States to act on pressing issues. This paper examines the deployment and strength of global health law instruments used by UN actors to call on Member States to restrict the exposure of children to unhealthy food and beverage marketing.MethodsGlobal health law instruments were identified from a review of four UN agencies that have a mandate over children’s exposure to marketing of unhealthy food and beverage products namely: the World Health Organization (WHO); the Food and Agriculture Organization (FAO); the United Nations General Assembly (UNGA) and the UN Office of the High Commissioner for Human Rights (OHCHR). Data on marketing restrictions were extracted and coded and descriptive qualitative content analysis was used to assess the strength of the instruments.ResultsA wide range of instruments have been used by the four agencies: seven by the WHO; two by the FAO; three by the UNGA; and eight by the UN human rights infrastructure. The UN human rights instruments used strong, consistent language and called for government regulations to be enacted in a directive manner. In contrast, the language calling for action by the WHO, FAO and UNGA was weaker, inconsistent, did not get stronger over time and varied according to the type of instrument used.ConclusionThis study suggests that a child rights-based approach to restricting unhealthy food and beverage marketing to children would be supported by strong human rights legal instruments and would allow for more directive recommendations to Member States than is currently provided by WHO, FAO and UNGA. Strengthening the directives in the instruments to clarify Member States’ obligations using both WHO and child rights mandates would increase the utility of global health law and UN actors’ influence.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12992-023-00939-4.