Many developers market apps for children as being educational. So Jenny Radesky, a pediatrician who wrote the American Academy of Pediatrics guidelines for children and media, wanted to check that out.

“One of my big concerns about why apps might not be educational was because of the presence of distracting features such as banner ads that sit along the top of the screen and which contain stimuli that are irrelevant to the learning objective,” Dr. Radesky said. “And we were expecting to see those.”

She was not expecting all the rest.

In apps marketed for children 5 and under in the Google Play store, there were pop-up ads with disturbing imagery. There were ads that no child could reasonably be expected to close out of, and which, when triggered, would send a player into more ads. Dancing treasure chests would give young players points for watching video ads, potentially endlessly. The vast majority of ads were not marked at all. Characters in children’s games gently pressured the kids to make purchases, a practice known as host-selling, banned in children’s TV programs in 1974 by the Federal Trade Commission. At other times an onscreen character would cry if the child did not buy something.

“The first word that comes to mind is furious,” said Dr. Radesky, an assistant professor of developmental behavioral pediatrics at the University of Michigan Medical School. “I’m a researcher. I want to stay objective. We started this study really just trying to look at distraction. My frustrated response is about all the surprising, potentially deceptive stuff we found.”