Appropriate nicotine levels, flavor restrictions and warning labels for cigarettes have long been a subject of national debate. One thing, however, has been near-certain ever since the risks of smoking became obvious: Tobacco shouldn't be sold to children. What, then, of the latest addictive threat on the scene? This is social media. Congress in recent days summoned representatives from YouTube, Snapchat parent company Snap and TikTok to Capitol Hill, after lawmakers spent most of a month with their fury trained on Facebook and its Instagram product. The subject of the Senate Commerce Committee hearing was "Protecting Kids Online," and the questions were pointed: Does TikTok's algorithm push teens toward content that glorifies eating disorders? As overdose deaths soar, what is Snap doing to stop drug dealers on its platform? How does YouTube avoid collecting data on users under the age of 13, especially when age verification is difficult? Regarding these diverse sites as a monolith would be a mistake. Yet they do, in their design to hold people's attention with a repository of third-party posts helped along by recommendation algorithms, have something in common. The sites also have something else in common: They're immensely popular among a rising generation — much more, indeed, than the name-brand app with which Facebook started its empire. Addressing the society-wide ills of social media may best be begun by addressing its ills among its youngest users. Early intervention could prevent problems that, left unaddressed, might become insoluble. And protecting kids, online or off, is generally something everyone can agree on. A proposal from Sens. Edward J. Markey (D-Mass.) and Bill Cassidy (R-La.) would seek to update the Children's Online Privacy Protection Act by raising the age for safeguards, as well as imposing limits on targeted advertising directed at those covered. Their bill would change the law to include children between the ages of 13 and 15. Another from Mr. Markey and Sen. Richard Blumenthal (D-Conn.), called the KIDS Act, would shelter consumers under 16 from "damaging design features" such as autoplay, push alerts and like counts. A provision barring the amplification of some harmful — but not illegal — content seems of dubious constitutionality; generally, however, the ideas are intriguing. The bills that legislators are touting today may not make it into law, but even in their absence, companies (prompted in part by Britain's new Age-Appropriate Design Code) are experimenting with child safety efforts.