The Federal Trade Commission on Thursday criticized Apple, Google and other tech firms for failing to be upfront with parents about how the companies are collecting personal data through mobile apps aimed at young children.

In a report, the FTC painted a portrait of a digital Wild West where children’s apps — such as nursery rhyme programs and alphabet software — on smartphones and tablets could violate the privacy of youth.

These programs are becoming more popular among children as mobile gadgets flood homes. In fact, the FTC found that the majority of apps promoted by Apple and Google are aimed at children.

Child privacy laws require online firms to get permission from parents to collect data about users under 13. Companies must also clearly explain what information is being collected, and how it is being shared or used for profits.

The FTC said that it would investigate specific app developers as well as Apple and Google to determine privacy violations.

The FTC said it surveyed about 1,000 apps designed for children on iTunes and the Android Marketplace by searching for the word “kid.” It said the companies could be tracking geolocation, phone numbers, contact lists, call logs and other “unique identifiers,” but they don’t make it easy for parents to figure this out.

Apple and Google rarely disclose information about data collection. And app developers provide precious little information about their privacy practices, the FTC said.

“Companies that operate in the mobile marketplace provide great benefits, but they must step up to the plate and provide easily accessible, basic information so that parents can make informed decisions about the apps their kids use,” FTC Chairman Jon Leibowitz said in a statement.

Apple and Google did not immediately respond to requests for comments about the report.

“Many children’s education app developers are unaware of privacy regulations and how they may be interpreted to prevent seemingly innocuous features,” said Morgan Reed, executive director of the Association for Competitive Technology, which represents app developers and other tech firms.

The FTC also said it is considering specific protections to guard children from ringing up huge bills when games or other apps encourage them to spend real money. For instance, some parents complained that their kids were spending $99 of real money for imaginary smurfberries in the popular Smurfs’ Village game.

“The ability of children to purchase items within mobile applications has been a subject of concern in media reports and by members of Congress, as parents may not know about such capabilities,” the FTC said in a report.

The FTC recommended that app developers provide simple and short disclosures on how they collect and share information about users, including whether their apps connect to social media sites such as Facebook. Parents should be told if kids’ apps contain advertisements, a concern of privacy groups who have protested mature ads and the promotion of goods such as junk food and concert tickets to kids.

“As gatekeepers of the apps marketplace, the app stores should do more,” the staff report suggested.

The FTC noted that apps stores create their own age ratings for apps. These guidelines are often not consistent or accurate, privacy advocates say.

And, according to public interest group Common Sense Media, ads and inappropriate content are at times deep within apps, seen only when a player reaches an advanced stage of a game.

“Consumers, especially children, should not have to contend with mobile phone spies,” said Jeff Chester, executive director of the Center for Digital Democracy, a privacy advocacy group. “Both Google and Apple, the two leading mobile app companies, must do a much better job protecting children’s privacy.”