If you’re looking for morals in many of today’s Hollywood movies geared toward 'tweens and teens, you might be hunting a long while.

In recent years, the line has been pushed further and further, as the film industry has challenged the ratings system by showing kids and teens racier, more politically incorrect movies.

“There has definitely been a slippage in terms of the kind of material that gets in under that PG or PG-13 rating,” said movie critic Michael Medved (search). “Material today … in the PG-13 category used to clearly be R.”

This season offers the sexually explicit “Catwoman,” the four-letter-word-laden “Anchorman” and the suggestive “Sleepover” — not to mention “The Notebook,” which is full of racy moments.

“There is shockingly graphic sex — really some very, very R-rated sex scenes,” said Medved of PG-13-rated “The Notebook.”

Even “A Cinderella Story,” starring Hilary Duff (search) — known for her apple pie, girl-next-door image — is full of negative characters.

“I’m growing up, and I obviously want to do more, take different kinds of roles,” Duff said. “It’s definitely important to move forward and do something that older people are going to enjoy.”

But the changes in film content means parents can’t rely on the ratings to tell them just what their teenage children are watching in movie theaters.

“It used to be that parents assumed if there is a PG movie or a PG-13 movie … it could have a little bit of racy stuff, but it’s OK for teens,” said Medved. "The problem is PG-13 is much closer to R than it is to PG. ... Anyone can get into a PG-13 movie without parental approval. ... There needs to be a change in the ratings system."

Medved said sometimes films' content serves to undermine lessons parents and schools are trying to teach children.

"If you look at high schools across the country, there's a lot of struggle going on and some evidence that that struggle is actually successful in educating kids for greater sexual responsibility, for more self-control," he said. "At the same time, the movies are sending out the message that teenage sexuality is not only happening, but it's happening for everyone."

The reality, according to the National Institutes for Health (search), is that teenage sexual activity is actually decreasing.

"More and more kids are maintaining their virginity, at least through high school," Medved said. "That is something Hollywood hasn't picked up at all."

Of course, studios realize that the blurred lines and a shifting ratings system can mean wider audience appeal, which translates into more ticket sales.

But filmmakers' perpetual quest to earn major profits makes it tough for parents to monitor what their kids are up to. And that's what frustrates people like Medved.

“No one believes that it’s the business of the entertainment industry to raise our kids,” he said. “That’s our job as parents. But the entertainment industry shouldn’t make it more difficult for us than it has to be.”

Fox News' Mike Waco and Catherine Donaldson-Evans contributed to this report.