TORONTO - For the follow-up to his Oscar-winning animated smash "Happy Feet," director George Miller pulled off a casting coup and brought Matt Damon and Brad Pitt aboard to portray a pair of quarrelling crustaceans.

But the Australian filmmaker can't really take the credit for landing the marquee stars.

"Their kids had seen the first 'Happy Feet,' so they didn't have to read the script," Miller, 66, said during a recent promotional trip to Toronto. "Their kids just said: 'You're doing this movie."'

And that mandate held, even though the new film required the pair of megastars to showcase their singing voices -- for better or worse.

"Matt Damon can sing and Brad Pitt definitely can't," said the bespectacled director with a laugh. "But he gave it a shot."

Now, Miller hopes audiences flock to the new 3D film at the same fleet-footed pace that the stars did.

The first "Happy Feet" was something of a surprise upon its release in 2006. Where most of the biggest computer-animated hits of recent years have come from Pixar or the Dreamworks-owned Pacific Data Images, "Happy Feet" was the inaugural feature-film production for the Australian digital visual effects company Animal Logic.

Still, its jaunty tunes, crackling choreography and a realistic visual style captured the imaginations of enough film-goers to propel the film toward worldwide grosses of nearly $400 million and an Academy Award win for best animated feature.

The first film focused on the Elijah Wood-voiced Mumble, a fluffy penguin whose search for a mate is stalled by his inability to sing. "Happy Feet Two" -- which opens Friday -- revolves around Mumble's son, Erik, who's cursed by a different foible: he's failed to inherit his father's dazzling dance moves. Other stars to lend their voices to the film include Robin Williams, Sofia Vergara and Alecia Moore (better known as the pop star Pink).

Miller reels off a series of improvements he was able to implement in the second film, from more complex dance sequences to the introduction of 3D, which is used primarily to add another layer of tactile depth to the film's lush creations (Miller, for one, is a fan of the technology, saying: "When I'd watch dailies, I hated seeing it in 2D.")

Miller is adamant that the film's depiction of its creatures and their habitat remain as realistic as possible (aside from, you know, all the singing, dancing and talking), so he used the advanced technology to more carefully render the film's critters and sparkling Antarctic environment.

"We base it as much as possible on the natural history of the world, so you'll notice that the water and the clouds and the sky and the ice and the shapes of the icebergs is very, very close to reality," he said.

Part of the reason the original "Happy Feet" resonated the way it did with some fans and critics was in its environmental message. "Happy Feet Two" hits some of the same notes, showcasing a penguin community thrown into peril by a major shift in their habitat.

The messaging is subtle and never overtly political, but Miller said it was important nonetheless.

"You can't tell the story of that world without looking at what's happening with the environment," he said.

"It is the canary in the coal mine. It's such a delicate environment at the extremes of the planet that any change is felt by all the creatures down there. So it's part of the world, it's part of the story."

"Happy Feet" was actually Miller's first foray into animated filmmaking. His long career initially took off when he wrote and directed the 1979 post-apocalyptic cult thriller "Mad Max" (which also introduced audiences to a fledgling Australian actor named Mel Gibson) as well as its two sequels.

He later helmed two more Oscar-nominated pics -- 1987's fantastical comedy "The Witches of Eastwick" and 1992's tragic medical drama "Lorenzo's Oil" -- before writing the 1995 surprise smash "Babe" and directing its sequel, "Babe: Pig in the City."

Now, he says he's hoping to begin shooting a long-gestating fourth "Mad Max" sequel "Fury Road" next year in Australia, with Tom Hardy, Charlize Theron and Nicholas Hoult set to star.

And he does feel ready to march in a different direction after spending the better part of a decade on his "Happy Feet" films. Miller has an astoundingly diverse resume, but even he didn't anticipate spending so much time with the adorable animals.

"It's a bit tragic that you spend so many years of your life animating penguins," he said with a wry grin.

"But here we are."