The U.S. Federal Trade Commission is investigating allegations that Google’s (GOOGL.O) YouTube violated rules about collecting data on and advertising to children, according to a person familiar with the matter.

The commission is probing whether the world’s largest video site broke the Children’s Online Privacy Protection Act, which makes it illegal to collect information on minors and disclose it to others without parental permission. A group of activists last year asked the FTC to look into the matter. Representatives for YouTube and the FTC declined to comment.

Amid the investigation, YouTube is considering more changes to how it handles content for kids, according to a different person familiar with the company’s discussions. The Wall Street Journal reported earlier Wednesday that the company was mulling moving all videos for children to its separate YouTube Kids app. Such a drastic change is unlikely, according to the person, who asked not to be identified discussing YouTube’s deliberations.

YouTube has faced rising criticism about content for children. The company has hired employees to specifically watch and vet videos for kids to root out harmful ones, and has pushed a kids-only app that is much safer.

Still, disturbing videos aimed at children had lived on the site for years until the end of 2017 when a burst of criticism got the company to focus more seriously on the issue. Before that, pushing up engagement was the main metric YouTube organized around, according to a Bloomberg investigation published in April. As for the kids-only app, data shows its usage by children is small compared with the main, unfiltered site.

Democratic Senator Ed Markey of Massachusetts, who was a key force behind the passage of COPPA, said in a statement that the probe was "long overdue."

"In the coming weeks, I will introduce legislation that will combat online design features that coerce children and create bad habits, commercialization and marketing that manipulate kids and push them into consumer culture, and the amplification of inappropriate and harmful content on the internet," Markey said.

In April, Markey outlined a bill that would rein in algorithms and other features that amplify harmful content on big tech platforms and establish rules for product placement.

Last year, a coalition of more than 20 child advocacy and privacy groups filed a complaint with the FTC, alleging YouTube knowingly collected data on and pushed ads to children younger than 13. YouTube technically doesn’t allow children to have accounts on the site but executives have acknowledged kids watch YouTube regularly.

The youth market in online content is hard to ignore for companies that generate sales from advertising on the web. YouTube doesn’t share sales, but the research firm Loup Ventures estimates that 5 per cent, or roughly US$750 million a year, of the video site’s annual revenue comes from content aimed at children.