Many researchers and organizations, such as WHO and UNICEF, have raised awareness of the dangers of advertisements targeted at children. While most existing laws only regulate ads on television that may reach children, lawmakers have been working on extending regulations to online advertising and, for example, forbid (e.g., the DSA) or restrict (e.g., the COPPA) advertising based on profiling to children. At first sight, ad platforms such as Google seem to protect children by not allowing advertisers to target their ads to users who are less than 18 years old. However, this paper shows that other targeting features can be exploited to reach children. For example, on YouTube, advertisers can target their ads to users watching a particular video through placement-based targeting, a form of contextual targeting. Hence, advertisers can target children by placing their ads in children-focused videos. Through a series of ad experiments, we show that placement-based targeting is possible on children-focused videos and enables marketing to children. In addition, our ad experiments show that advertisers can use targeting based on profiling (e.g., interest, location, behavior) in combination with placement-based advertising on children-focused videos. We discuss the lawfulness of these two practices concerning DSA and COPPA. Finally, we investigate to which extent real-world advertisers are employing placement-based targeting to reach children with ads on YouTube. We propose a measurement methodology consisting of building a Chrome extension to capture ads and instrument six browser profiles to watch children-focused videos. Our results show that 7% of ads that appear in the children-focused videos we test use placement-based targeting. Hence, targeting children with ads on YouTube is not only hypothetically possible but also occurs in practice...

翻译：许多研究者和世界卫生组织（WHO）、联合国儿童基金会（UNICEF）等机构已多次警示针对儿童的广告风险。尽管现行法律主要规范可能触达儿童的电视广告，立法者正致力于将监管范围扩展至网络广告领域，例如禁止（如《数字服务法》DSA）或限制（如《儿童在线隐私保护法》COPPA）基于用户画像的儿童广告。表面上，Google等广告平台通过禁止广告主向未满18周岁用户投放定向广告来保护儿童。然而，本文揭示了其他可被利用以触达儿童的定向功能。例如，在YouTube平台上，广告主可通过"投放位定向"——一种情境定向形式——将广告定向至观看特定视频的用户。因此，广告主可通过在儿童内容视频中投放广告来实现对儿童的营销。通过系列广告实验，我们证明在儿童内容视频上进行投放位定向具有可行性，并可实现针对儿童的营销。此外，实验表明广告主可在儿童内容视频中将基于画像的定向（如兴趣、位置、行为）与投放位广告结合使用。本文就这两种做法在DSA和COPPA框架下的合规性展开讨论。最后，我们探究了现实世界中广告主在YouTube上通过投放位定向触达儿童的真实程度。我们提出了一套测量方法：构建Chrome扩展程序捕获广告，并配置六个浏览器配置文件观看儿童内容视频。研究结果显示，在测试的儿童内容视频中，7%的广告采用了投放位定向策略。这表明在YouTube上针对儿童的广告投放不仅是理论可能，现实中亦已发生……