Correction: An earlier version of this article misidentified the executive director of the Association for Competitive Technology. He is Morgan Reed, not Reed Morgan. This version has been corrected.

If gun-toting zombie killers, lewd language or busty women prowling for “hot guys” got on children’s TV shows, parents would run to the federal government’s indecency patrol in protest.

But such content is finding its way onto mobile applications aimed at children, who are spending more and more time tapping away on smartphones, iPods and other gadgets.

Amid an explosion of kid-oriented apps for mobile devices, frustrated parents say they face an uphill battle guarding the Internet’s youngest users from inappropriate content. They complain of unreliable age and maturity ratings made by mobile software developers, sexually explicit and violent ads that show up on kids’ games, and a lack of rules to keep the massive apps industry in check.

“This is the platform of the future, and as of now it is a free-for-all, a total Wild, Wild West,” said Jim Steyer, president of children’s media advocacy group Common Sense Media, which rates mobile apps because it thinks companies’ efforts fall short.

It’s far less wild for traditional media. The Federal Communications Commission patrols the airwaves for curse words and sexual content during prime viewing hours. Hollywood’s trade group created a board to assign maturity ratings for all U.S. movies. Video-game makers do the same, even though they fight against state and federal labeling rules.

But when it comes to mobile apps, developers give themselves ratings. And the guidelines are often confusing. What constitutes “low maturity” or “medium maturity” on phones that run Google’s Android? A Google Web site states that profanity and references to drugs and sex are permitted for “medium maturity” apps, but would a parent know that from the label?

Aside from confusing ratings, there are many inaccuracies, Steyer and others say.

That was the case for Ingrid Simone, whose 5-year-old son Lawrence Patrick recently came across frightening circular saws that dismembered players of the snowboarding game iStunt 2.

The game was rated for players as young as 4, according to developer MiniClip on the Apple iTunes store. It looked harmless from the game description and still images presented at the time. So Ingrid downloaded it onto the family iPad.

“We felt like we did everything right,” Simone said. “Nowhere at the time was there any warning of the violence that came later on.” MiniClip has since added a preview image of the saws.

Some parents say they often disagree with ratings offered by developers.

On Android devices, Boy Facts is rated “low maturity,” which appears safe for older children. Yet it offers advice about how to deal with men, including “many things about sex, couple life, etc.” Despite touting lessons on how to “seduce” the “guy of your dreams,” 101 Secrets About Guys doesn’t have a maturity rating.

Resident Evil for the iPhone is rated for age 9 and older, and players wield guns to kill “blood thirsty” red-eyed zombies and monsters. (The version for video-game consoles such as the Xbox is rated for players 17 and older, though it is more violent.)

Ads for other apps that are much more mature can pop up on kid-focused mobile programs. Racing Penguin, a popular iTunes app, is aimed at users as young as 4. But players are served up ads for Top Girl, which proclaims: “Do gigs, shop, dress, go clubbing, and flirt with HOT guys!”

Top Free Games, the developers of Racing Penguin, said it doesn’t control the ads that appear on their free games. They say Apple’s and Google’s mobile ads services choose what is served up to apps.

Apple said it gives parents the ability to protect children with settings on devices that restrict app downloads.

“We are proud to have industry-leading parental controls . . . parents can easily use parental control settings,” Apple spokeswoman Trudy Muller said.

Google declined several requests to comment for this article.

Federal lawmakers are contemplating rules to block bullying, adult predators and companies that want to collect personal information about minors through mobile apps. But none of the proposed rules address content and indecency issues, even though some programs are aimed at newborns and toddlers.

App developers argue that they are in the best position to monitor their own content. After all, what is considered sexually explicit in the United States — nudity, for example — might not be offensive in Europe, said Morgan Reed, executive director for the Association for Competitive Technology, a trade group for app developers and other high-tech firms.

“What you don’t want to do is paint too broad a brush with regulation that will do more harm than good,” Morgan said.

Mobile devices have become mainstream for teens, and younger children are increasingly using mobile phones, experts say. Three in 10 children between the ages of 8 and 10 have their own phone. That number jumps to seven in 10 for children ages 11 to 14, according to a study by Kaiser Family Foundation.

And children younger than 12 are spending 11 hours a week online, up 63 percent from 2004, according to Nielsen research. Much of that time is on mobile devices, experts say.

In a hearing on children’s online privacy this month, lawmakers expressed their anxieties about mobile apps.

“The thing about television is that you can walk across the room and get a sense of the show,” Rep. Bill Cassidy (R-La.) said during the House Commerce, Trade and Manufacturing Subcommittee hearing.

But when Cassidy tried to control his 10-year-old daughter’s use of mobile applications, he said he felt “disempowered,” because there have been instances when he thought something looked age-appropriate “but then it takes you places that look very different.”

“Developments are happening so quickly in the digital marketing industry that many of the new techniques may be escaping scrutiny,” Kathryn Montgomery, a professor of communications at American University known for her contribution to the 1998 Children’s Online Privacy Protection Act, said at the hearing.

Part of the challenge is that the most popular games for adults and children are usually animated.

That confuses children such as Berna Erol’s 5-year-old son, who regularly searches the iTunes app store and inadvertently has asked his parents to download war games and sexually explicit apps because of their cartoon characters.

Erol carefully screens apps, won’t give him her password and sets clear rules for the kinds of videos he can watch on Netflix over his iPod. But those precautions ­haven’t prevented him from trolling the apps store and viewing racy or bloody video descriptions and screen shots.

“Devices create a very private environment for children. They are watching on a small screen, listening through earphones. So it is up to parents to be even more vigilant,” Erol said.