Children's online experience, especially the risks to which they might be exposed, is an increasingly important policy and research concern. This article reports an analysis of the amount, nature and range of empirical research concerning children's online experiences across 18 European countries. Research teams in each country have collaborated, as part of the "EU Kids Online" network, to identify, code and compare studies. In all, 235 studies were identified and coded in a publicly accessible data repository. All countries had some available evidence regarding children's online risky experiences, with strengths mainly in relation to research into access and use; several countries were found to have a richer evidence base encompassing research into online learning, literacy, participation, parental mediation and so forth. Regarding risks, more research focused on potentially harmful content than on risky forms of contact. Key research gaps included research on younger children, into mobile online platforms, and into certain types of online risk. The article concludes by observing the challenges facing researchers in this field, including the time-sensitivity of research that quickly dates, the difficulty of tailoring research to meet the needs of a demanding policy agenda, the complexity of designing projects that recognise the contextual and contingent factors that mediate children's online activities, and the ethical considerations that apply when asking children about private, transgressive or upsetting experiences.