The study assessed 135 kids apps geared towards kids five years old or younger, and it found that 95 percent had at least one type of advertising. In one app, for example, players trying to treat sick animals are told that they can get more effective medicines if they watch an ad. In another, a character encourages players to put on clothing that has to be unlocked by an in-app purchase. The Senators said that the "manipulative nature" of these sorts of ads concerned them, as did the fact that over 93 percent of the apps billed as educational included advertising. They also took issue with apps characterized as free but required in-app purchases to fully enjoy.

Advertising isn't the only issue that's been brought up when it comes to apps for kids. In the past, such apps have been found to be improperly collecting children's data, listening to what kids watch and serving up porn ads.

The lawmakers said that the examples included in the study "appear to constitute unfair and deceptive practices under Section 5 of the Federal Trade Commission Act." They asked the FTC to look into the study's findings and requested a response to their letter by December 4th.