Rising to the challenge: Introducing protocols to monitor food marketing to children from the World Health Organization Regional Office for Europe.

Unhealthy marketing has been unequivocally linked to children's food preferences, requests, purchases and eating behaviors and hence to childhood obesity. Regulating children's exposure to such marketing has been identified as a key challenge to which States must rise. Regulation mandates the need for monitoring and hence for credible data that are comparable between countries, regions and across time. However, there are major challenges presented by the complexity of the digital marketing ecosystem including the personalized targeting with persuasive, exploitative advertising to which children are subject. This narrative review identifies challenges faced by researchers in the digital ecosystem; reviews recent papers attempting to address these and specifies benefits and limitations; and introduces a set of WHO protocols with templates and guidance for studies of food marketing to children.