Advocacy groups on Wednesday renewed their call for the Federal Trade Commission to investigate whether YouTube was serving behaviorally targeted ads to children under the age of 13.

“Ultimately, only a body with investigative authority, such as the Commission, can conclusively determine whether Google and YouTube are engaging in behavioral advertising,” Fairplay (formerly Campaign for a Commercial-Free Childhood), the Center for Digital Democracy, Common Sense Media and the Electronic Privacy Information Center write in a 92-page request to the agency.

The groups’ request comes one week after Adalytics reported that YouTube sets cookies on the devices of viewers who watch “made for kids” videos.

Adalytics specifically said Google “has been observed to appear to” set “long-lasting ‘advertising’ related cookies on the browsers of consumers watching YouTube videos that are clearly labeled as ‘for kids.’”

Cookies can be used to track web users and serve them with personalized ads — which could potentially violate the federal Children’s Online Privacy Protection Act (COPPA). That law effectively prohibits businesses from knowingly deploying behavioral advertising techniques on children younger than 13, without parental consent.

Google denies tracking people who watch “made for kids” videos, noting that cookies can be used for analytics, fraud prevention and other ad-related activity that doesn’t violate the children’s privacy law.

Fairplay tells the FTC it conducted its own test of YouTube, and concluded that it may be serving behaviorally targeted ads on videos aimed at children.

For the test, Fairplay said it paid $10 to run a total of 1,446 ad impressions across across 46 “made for kids” channels including Miraculous Ladybug and CVS 3D Rhymes and Kids’ Song.

Fairplay also selected ad-targeting categories such as “motorcycle enthusiasts,” “retiring soon” and “cloud service power users.”

An audience segment report sent by Google to Fairplay said ads reached people in those categories.

“For example, 432 of those 1,466 ad impressions came from users identified by Google as ‘motorcycle enthusiasts,’ and 70 impressions came from ‘cloud services power users,’” Fairplay and the others say in their request for an FTC investigation.

The groups add that Google shouldn’t have been able to report that the ads were viewed by users based on their inferred interests, given that the company says it doesn’t use behavioral targeting techniques on children.

But Google — which previously paid $170 million to settle charges that YouTube violated COPPA — says Fairplay “appears to have jumped to the incorrect conclusion.”

The company also says its “made for kids” channels can have a mix of content for children and content for adults.

“The audience segment report that they received back does not indicate that personalization took place on made for kids videos,” Google writes. “Without being able to review the full details of this campaign and all of its targeting criteria, it is possible that these channels have not-made for kids videos (as described above given many channels have a mix of content types), and that may be the source of this reporting.”

Advocacy groups on Wednesday renewed their call for the FTC to investigate whether YouTube was serving behaviorally targeted ads to children under the age of 13.