Abstract Background The online world affords children many benefits, such as connectivity and access to educational and cultural content. Simultaneously, it increases their likelihood of encountering harmful or distressing web-based content and behaviour, such as marketing for harmful products, violent or discriminatory material, and cyberbullying. Yet, there is a dearth of objective research globally on children’s real-time experiences, with current research relying on self-reports or observations made in experimental conditions. This paper reports on the nature and extent of children’s online world. Methods Kids Online Aotearoa is a cross-sectional observational study of children’s real-time experiences of the online world. A strategic sample of 180 12-year-olds from schools in the Wellington region of Aotearoa, New Zealand, used Zoom video conferencing software to record their online world for four days. Recordings were analysed manually and using AI. Results Children spend most of their time online on their phones, often using TikTok. Children spend 25 % of their online phone time gaming or watching games (game time). They encounter many gambling and gambling-like activities while doing so. Of game time, 16% of the time children are exposed to marketing. Preliminary analysis reveals that children are exposed to marketing for alcohol, junk food, tobacco, vapes and gambling. This is counter to national legislation prohibiting or restricting such marketing to children. Conclusions This novel methodology reveals the actual online experiences of children as they go about their daily lives. This includes engaging in harmful behaviours such as gambling and encountering harmful product marketing. While from New Zealand, this study is likely to be relevant for other countries given the global reach of the online world. The research indicates the urgent need for national and global government regulation of the online world to protect the rights of children and ensure their wellbeing. Key messages • Kids Online Aotearoa reveals the nature and extent of children’s online world, including their exposure to harmful product marketing. • National and global regulation of the online world is urgently needed to protect child rights and wellbeing.