Joey Pollari, the lead in MTV’s newest live-action series “The Inbetweeners,” was 16 when he shot the pilot. But by the time the show got picked up and a second episode was filmed, a couple years had passed — not a big deal for most adult actors, but a potential problem for a growing teen.

“Fortunately, Joe’s face didn’t change,” says exec producer Brad Copeland. “His voice got a little deeper. He did shoot up like 4 inches. We had to buy him new pants.”

The risks inherent in making TV for and starring kids are obvious: Your stars mature in unexpected ways and at unexpected speeds. And the changes aren’t just visual either. Some decide to move on to other kinds of roles before their properties have run their course, as when Daniel Radcliffe took a break from playing Harry Potter to play “Equus” on Broadway. Others make off-camera choices that belie their more innocent onscreen image, as when Jamie Lynn Spears’ pregnancy hastened the end of her run with “Zoey 101.”

Anyone taking on a young-talent-dependent series at any network assumes those risks — and knows the series’ longevity depends on a teen star not changing too much, too fast. That’s enough to make any showrunner or exec nervous, potentially putting them at the mercy of their young cast (how long can “Glee” keep its cast in high school?). Still, every network seems to deal with the potential problems differently.

ABC Family executive VP of original series and development Kate Juergens takes the practical outlook. “We understand we only get these talented people for a short window in their lives — and then they go on to something else.”

When they do, their series — if not ensemble-based and frequently repopulated with fresh faces — typically goes with them. That doesn’t necessarily make much sense in the grand budgetary scheme of things.

“Having a long-running show is cost-effective,” says Kate Taylor, senior executive producer of children’s programming at PBS affiliate WGBH. “All of the hard early development costs and effort we put in early means you can amortize what you’ve already done. The kids grow up, but a new batch comes along.” And the show lives on.

That’s a lesson the 33-year-old “Degrassi” franchise learned early on, but by accident. “It was never a master plan” to endure for decades, says franchise co-creator and Epitome Pictures CEO Linda Schuyler. “It evolved as we went along.” But when showrunners tried to carry the “Degrassi” name with beloved characters to the university level, “interest in the characters plummeted,” she says. “Ever since then, we’ve seeded the cast every year with new (students).”

That’s the long-term plan for Brenda Hampton’s “Secret Life of the American Teenager” on ABC Family. “The show is the star of the show, not one particular actor,” she says. “Hopefully, someone is going to get a career boost from the show, but you also want the show to survive and go on if they pop and go forward.”

The dedicated kids’ networks of Disney Channel and Nickelodeon don’t necessarily share the same expecations when developping their shows. That they’ve had kid stars who grew up and exited (and thus ended) their star vehicles is just considered the cost of doing business: Disney got four seasons out of Miley Cyrus for “Hannah Montana” (plus a movie); Nickelodeon got six out of Miranda Cosgrove on “iCarly” (she also had a prominent role on the Nick series “Drake & Josh” prior to “iCarly”). And that does not seem to worry them at all.

“Most of our live-action shows go for 60 episodes,” says Marjorie Cohn, president of development and original programming for Nickelodeon. “If they go beyond that, yay, but that’s the norm, not the exception.”

Amortizing and cost-benefit analyses don’t matter much under that model. According to Cohn, the network knows what young viewers want, and it’s always something new, something different. “Kids want a show that belongs to them,” she says. “They don’t want their big brother’s show; they want their own show.”

Disney Channel is also happy with its typical four-season runs, hewing almost to the old-fashioned studio system of keeping talented young actors inhouse. “On Disney Channel, the stars are the franchises,” says Adam Bonnett, senior veep of original programming. “Every character has a journey, and sometimes that journey ends after three or four seasons. But if a star ages up and out of our demographic, we’ll find something new for them.”

That’s true for both networks: Just as Cosgrove graduated from “Drake & Josh” to “iCarly,” Disney Channel’s Debby Ryan aged out of “The Suite Life on Deck” and into a series as a nanny in “Jessie.” “Debby Ryan loves being a Disney Channel star and wants to continue being one,” Bonnett says. “The challenge is to come up with a concept to make sure she still works on the Disney Channel.”

Meanwhile, over on the broadcast side, producers are so happy just to get picked up from pilot and then granted an additional season or two that no one has time to worry about what may become of their child stars down the line.

“It’s a high-class problem if a 12-year-old has become a 16-year-old in this business,” says Christopher Lloyd, co-creator and exec producer on ABC’s “Modern Family.” “I hope that’s the biggest problem I’m facing six years from now.”

Sudden hair changes (as are the wont of teenagers) seem to be the biggest issue broadcast network series producers and network executives have to deal with when it comes to young actors. “That’s definitely one of their concerns,” says Jason Katims, showrunner of NBC’s “Parenthood.” “And rightfully so: You want to make sure the way actors appear is consistent.”

But talent such as “Two and a Half Men’s” Angus T. Jones (who has hinted that he’s ready to move on a few times in the past) do have a tendency to outgrow their shows eventually, especially if they’re serious about sticking with acting, lest they end up pigeon-holed by a childhood role.

Eileen Heisler, showrunner and co-creator at ABC’s “The Middle” agrees that when working with kids, “you have to have a little bit of blinders on. We don’t make extreme long-range plans. When you’re working with kids, you know they’re going to change. Whether it’s on a cable kid-centric network or a show for one of the broadcast networks, that’s just the understanding. Kids change.”