Parents beware: Many YouTube channels that are wildly popular with young children are targeting them with thinly veiled ads for sugary beverages and junk food.

That is the conclusion of a new study published in the journal Pediatrics. The study authors analyzed more than 400 YouTube videos featuring so-called kid influencers — children with large social media followings who star in videos that show them excitedly reviewing toys, unwrapping presents and playing games. The study found that videos in this genre, which attract millions of followers and rack up billions of views, were awash in endorsements and product placements for brands like McDonald’s, Carl’s Jr., Hershey’s, Chuck E. Cheese and Taco Bell.

About 90% of the foods featured in the YouTube videos were unhealthy items like milkshakes, French fries, soft drinks and cheeseburgers emblazoned with fast food logos. The researchers said their findings were concerning because of YouTube’s popularity. Roughly 80% of parents with children 11 years old or younger say they let their children watch YouTube, and 35% say their children watch it regularly.

A spokeswoman for YouTube said the company had “invested significantly in the creation of the YouTube Kids app” and that “we don’t allow paid promotional content on YouTube Kids.”

Young children are particularly susceptible to marketing. Studies show that children are unable to distinguish between commercials and cartoons until they are 8 or 9 and that they are more likely to prefer unhealthy foods and beverages after seeing advertisements for them.

Experts say it is not just an advertising issue but a public health concern. Nearly 20% of Americans ages 2 to 19 are obese, up from 5.5% in the mid-1970s. Studies have found strong links between junk food marketing and childhood obesity, and experts say that children are now at even greater risk during a pandemic that has led to school closings, increased screen time and sedentary behavior.

“The way these branded products are integrated in everyday life in these videos is pretty creative and unbelievable,” said Marie Bragg, an author of the study and an assistant professor of public health and nutrition at the New York University School of Global Public Health. “It’s a stealthy and powerful way of getting these unhealthy products in front of kids’ eyeballs.”

Bragg was prompted to study the phenomenon after one of her co-authors, Amaal Alruwaily, noticed her nieces and nephews obsessively watching YouTube videos of “kidfluencers” like Ryan Kaji, the 9-year-old star of Ryan’s World, a channel with 27 million subscribers. Children’s channels like Ryan’s World — which are frequently paid to promote products — are among the highest-grossing channels on YouTube. According to Forbes, Ryan earned $26 million last year, making him the top YouTube earner of 2019. Among the brands he has been paid to promote are Chuck E. Cheese, Walmart, Hasbro, Lunchables and Hardee’s and Carl’s Jr. One video shows him pretending to be a cashier at McDonald’s. It has been viewed about 95 million times.

Sunlight Entertainment, the production company for Ryan’s World, said it “cares deeply about the well-being of our viewers.”

To document the extent of the phenomenon, Bragg and her colleagues identified five of the top kid influencers on YouTube, including Ryan, and analyzed 418 of their videos. They found that food or beverages were featured 271 times, and 90% of them were “unhealthy branded items.” The videos featuring junk food have collectively been viewed more than 1 billion times.

The researchers could not always tell which products the influencers were paid to promote. The Federal Trade Commission has said that influencers should “clearly and conspicuously” disclose their financial relationships. But critics say the policy is rarely enforced.

Last year, senators called on the FTC to investigate Ryan’s World. The Council of Better Business Bureaus also found that Ryan’s World featured sponsored content from advertisers without proper disclosures. And watchdog group Truth in Advertising filed a complaint accusing the channel of deceiving children through “sponsored videos that often have the look and feel of organic content.”