Google introduced YouTube Kids in February as a mobile app “built from the ground up with little ones in mind,” according to a blog post by the company. The app is geared for children of preschool age and older. After downloading the app on a mobile device, parents are guided through a tour of how to set safety features, like the option to block searching. The videos on the platform are selected from the main YouTube site through algorithms set to pick child-related content.

The groups expand on their April complaints by asking the F.T.C. to examine the advertising practices of food companies, and by citing new evidence of junk food ads on the app. In the new complaint, the groups argue that more than a dozen food companies have fallen short of their own promises to abstain from marketing junk food to children on YouTube Kids. The groups say that brands like Burger King, Coca-Cola, ConAgra Foods and American Licorice have commercials on the app for products including potato chips and chocolate bars.

While the groups direct blame toward marketers, they also criticize YouTube for not enforcing its own policies. YouTube restricts paid advertising of food and beverages on its children’s app, but the groups said their review of the app found many examples in which food companies used their own branded channels to show promotional videos. The groups asked for an investigation into uploaded TV commercials from unknown YouTube Kids accounts to determine whether there were connections between the food companies and those channels.

The Federal Trade Commission has been reviewing the April complaint, according to a person with knowledge of the investigation who spoke on the condition of anonymity. The F.T.C. usually accepts complaints and begins at least a preliminary review process.

Any investigation of the previous complaint and the new filings would not be public, said Jessica Rich, director of the Bureau of Consumer Protection at the F.T.C. “We welcome and we review carefully all such complaints submitted to us,” she added.