The EU announced investigations on Thursday into YouTube and TikTok to find out what action the US and Chinese-owned platforms are taking to ensure the safety of minors.
The European Commission said it had sent formal requests for information to TikTok and YouTube respectively, the first step in procedures launched under the EU's new law on digital content.
The EU's executive arm said it wanted to know what measures the video-sharing platforms have taken to comply with the Digital Services Act (DSA), especially regarding the risks posed to children's mental and physical health.
The DSA is part of the European Union's powerful armoury to bring big tech to heel, and demands that digital giants do more to counter the spread of illegal and harmful content as well as disinformation.
Platforms face fines that can go up to six percent of global turnover for violations.
TikTok, owned by Chinese company ByteDance, is particularly popular with younger users, while YouTube is part of the Alphabet digital empire that includes Google.
Both companies must respond by November 30.
The EU's top tech enforcer, Thierry Breton, said in August that "child protection will be an enforcement priority" for the DSA.
The law has also banned targeted advertising to minors aged 17 and under.
The EU already launched probes into TikTok, X (formerly Twitter) and Facebook-parent Meta over disinformation following the October 7 Hamas attack in Israel.
TikTok CEO Shou Zi Chew met EU officials earlier this week in Brussels, in talks the company's spokesperson on Thursday hailed as "positive".
"We're pleased that our efforts to keep people on TikTok safe, engage with these important topics and comply with the DSA, have not gone unnoticed.
"We will continue to work closely with the Commission, including on this latest request," the spokesperson said in a statement.
- Stricter curbs -
The DSA also demands tech behemoths do more to counter the spread of illegal goods.
The commission on Monday announced it kickstarted an investigation into China's AliExpress over what actions it is taking to protect consumers online from illegal products, including fake medicines, as part of DSA compliance.
The DSA came into force in August for 19 sites designated by the EU as "very large" platforms that have more than 45 million monthly active users, including Google Search, Facebook, Instagram, TikTok, YouTube, Amazon and Apple's AppStore.
Smaller digital firms will have to comply with the DSA from February next year, when EU member states will have set up national supervisory authorities.
TikTok and YouTube are also among 22 services listed by the EU in September that face stricter curbs on how they do business under the DSA's sister law, the Digital Markets Act (DMA). Companies must fully comply with the DMA by March 2024.