MTV and Nickelodeon — the rowdy siblings of the Paramount family — are now sitting at the adult table.

Long relegated to churning out low-cost pics aimed at young moviegoers, MTV and Nick are being transformed into big-time players.

MTV’s prepping “The Longest Yard” with Adam Sandler and “Aeon Flux” with Charlize Theron; Nick’s in production on potential franchise tentpole “Lemony Snicket’s Series of Unfortunate Events.” And both have been ramping up development in recent months.

MTV and Nick aren’t the only production shingles on these films but their newfound prominence is well-timed because it coincides with what Paramount brass are describing as the studio’s reinvention.

Studio chief Sherry Lansing and president Donald De Line have been telling the town and producers on the lot that Paramount’s shedding its risk-adverse rep to swing for the fences financially and artistically.

MTV and Nick execs, who have complained in the past that the Jonathan Dolgen-Lansing regime nixed many of their most interesting ideas, hope the new Par will be a better fit among the parts of the Viacom family.

No one’s been surprised at past differences, given that the style of Tom Freston and his MTV charges — relentlessly pursuing the Next Hip Thing — has been more freewheeling and idiosyncratic than the stolid Paramount culture.

Paramount’s new approach isn’t viewed as a mandate for MTV and Nick to greenlight projects on their own and become uber-producers like Scott Rudin or Brian Grazer.

But it does mean they’re being pushed to do much more than fill their usual niche at a time when Paramount’s no longer as tight-fisted as it’s been in the past.

“We want MTV and Nick to make movies that not only go to their target but expand the breadth of their audience,” says De Line.

“We want to see them do a full complement of films and we want them to do more. They both are incredible brands so we think they can go a lot further in terms of fully exploiting their capabilities.”

The consensus is that MTV and Nick have a decent reputation of connecting with their core audiences at a time when youth-oriented films are becoming the dominant type of movie. And that’s particularly crucial when marketing costs are going through the roof.

For Paramount, giving MTV and Nick more clout could be a way out of the box it’s been in for quite a while. The studio hasn’t released a $200 million grosser since “Mission: Impossible 2” four years ago; betting on the ability of MTV and Nick to deliver youth audiences seems sensible.

MTV Films exec VP David Gale isn’t surprised by his shingle’s elevated status.

“We’ve been a little under the radar but we’ve also released two to four films each year for the past seven years,” he notes. “So we’ve become gradually more and more credible, which is expanding the kind of films we’re developing.”

Gale believes Paramount has realized that the youth audience is the most reliable part of the moviegoing business, he notes.

And the two-decade link between MTV cable channels and its audience isn’t something that’s come about by accident but from a top-notch research department.

“One of our key components is having people who understand where tastes are going so we can be fresh rather than derivative,” Gale notes. “So it makes sense that we’re involved with films like ‘The Longest Yard’ and ‘Aeon Flux.’ ”

There’s still plenty of skepticism as to whether MTV and Nick can move beyond niche players.

“Every production company brings something different to the table and those two are perceived as being strong at marketing,” one agent explains. “They really know how to sell but they aren’t taken as seriously as major producers yet.”

Paramount, which brought on DreamWorks as co-producer of “Snicket,” is hoping for its own “Harry Potter”-style franchise since the Daniel Handler books about a set of orphans have tapped into the same preteen fan base as J.K. Rowling’s “Potter” tomes. “Snicket” has a darker tone than “Potter” and is set to open in December with the tagline “Taking the cheer out of Christmas.”

“‘Lemony Snicket’ is a gamble that’s out of character for Nick,” one agent observes. “If it succeeds, it will go a long way toward making people take Nick seriously.”

The studio’s already considering a second “Lemony Snicket,” De Line acknowledges, though nothing definite is in place.

MTV has managed unexpected successes like “The Kings of Comedy,” “Varsity Blues,” “Save the Last Dance” and “Jackass the Movie.” It’s wrapping up a Samuel L. Jackson basketball drama “All Day Long,” expected out by the end of the year; both “Aeon Flux” and “The Longest Yard” are scheduled to start shooting in July.

Nick, which broke out with bigscreen versions of “Jimmy Neutron” and “Rugrats,” should have another solid hit this November with its movie version of “SpongeBob SquarePants” on a relatively low budget. Nick Films exec VP Julia Pistor says the shingle has a finely honed understanding of its audience thanks to the day-to-day operations of its cable network.

“We have to be experts on kids because there’s so much competition for their attention,” she adds. “We have to get what our audience is in to, down to what kind of clothes they wear, or we won’t have credibility with them.”

Agents and producers admit that they’re still not used to taking top projects first to MTV and Nick. “Both MTV and Nick have come a long way,” one producer says. “If someone had said five years ago that they’d be where they are now, it would have seemed unbelievable.”

The Viacom-owned cable channels formed the two film units 11 years ago to produce movies for Paramount. “Beavis and Butt-head Do America” was a big early success for MTV; Nick launched modestly with “Harriet the Spy” and “Good Burger.”

Most MTV and Nick films have been profitable, although there have been a few misses like “The Perfect Score.” “Election” remains a major disappointment since it was critically acclaimed to the point of winning an Oscar screenplay nomination in 1999 but was only able to gross $14.9 million.

Paramount’s tight-fisted approach also meant many promising MTV/Nick projects have never advanced past the development stage. That may be changing as the door swings open for larger but still offbeat films.

MTV’s key projects are an oddball mix of genres:

  • an updated version of “The Warriors” with Tony Scott directing;

  • a “Car Show” comedy project, set in the world of customized cars and taking advantage of MTV’s cable hit “Pimp My Ride”;

  • Johnny Knoxville’s “Hot Dog” comedy about competing hot dog vendors in Los Angeles;

  • horror-thriller “Lost Girls,” set at a high-class reformatory in the Bahamas; and

  • “Genius,” in which an everyday guy is mistaken as a genius.

Nick — the younger and milder version of MTV — is adhering to its strategy of picking up strong lit properties such as “Snicket,” which it acquired in 1999.

Highest-profile is “The Spiderwick Chronicles,” based on a series of books about the fantasy world discovered by a trio of siblings. David Berenbaum (“Elf”) is writing the script. Pistor believes “Spiderwick” has a shot at being a franchise.

The rest of Nick’s development slate is dominated by the offbeat:

  • Its 3-D cartoon, Steve Oedekerk’s “The Barnyard,” set for release in late 2005;

  • CGI action-comedy “Mighty Mouse” with director-producer John Woo;

  • Klasky-Csupo’s “Green Monkeys,” based on the comic book by Mickey and Betty Parskevas about monkeys who think they’re human;

  • Supernatural action-adventure “The Mark” with Will Smith;

  • “Widow’s Broom” based on a book by Chris Van Allsburg in which a witch’s broom helps a grieving family and

  • “Alien Pets,” based on a book by Keith Graves in which a boy who’s inattentive to his own pets is forced to become a pet for outer space aliens.