IGNORANCE is bliss, especially for the computer-animated creatures in Ice Age 2: The Meltdown, Carlos Saldanha's energetic family adventure that will probably leave older audiences feeling a tad chilly.

The big freeze is coming to an end and the four-legged denizens are delighted by the newly-formed water features in the melting paradise that is their world.

Little do the critters realise that the towering wall of ice that encircles the valley is acting like a dam, holding back the floodwaters.

When armadillo con artist Fast Tony (voiced by Leno) lets the proverbial cat out of the bag, pandemonium ensures, and Manny the woolly mammoth (Romano), Sid the sloth (Leguizamo) and Diego the sabre-toothed tiger (Leary) join the mass exodus to escape the imminent deluge.

En route, the dysfunctional trio meets the one surviving female mammoth Ellie (Latifah), who thinks she is a possum, and her mischievous 'brothers' Crash (Scott) and Eddie (Peck).

The group heads for higher ground, followed every step of the way by Cretaceous and Maelstrom, a pair of prehistoric reptiles, who have defrosted from their icy prison and are now hungry for fresh meat.

As in the original Ice Age, the fractured central storyline is neatly book-marked by comical interludes with Scrat the sabre-toothed squirrel in relentless pursuit of a tasty acorn.

These hysterical sequences range from the deceptively simple (Scrat using a tree branch to pole-vault across a crevasse) to deliriously elaborate affairs, both above and below the ice floes.

Invariably, all of the tenacious critter's exertions end in failure, with the acorn slipping through his tiny claws. Bless.

Director Saldanha and his team opt for a series of polished set pieces rather than a fluid and coherent narrative, developing the characters in only the most simplistic terms.

Manny and Ellie's romantic subplot is pure treacle by the closing credits; valuable life lessons - overcome your fears, cherish your friends, believe in yourself - underpin every scene.

Peter Gaulke, Gerry Swallow and Jim Hecht's screenplay plies obvious puns and word play ('Don't that put the stink in extinct!'), with surprisingly few pop culture references.

Humour is skewed very young, delighting in Sid's bodily functions ('I did something involuntary... and messy!') and the misfortune of a character getting its tongue stuck to the ice, then swinging, bungee-style, from the distended pink muscle.

The quality of the computer animation has improved immeasurably from the first film, especially in the small details like the movement of the mammoths' fur in the breeze or the way light refracts through a melting icicle.

Characters possess realistic weight and inertia, but are still cartoonish enough that Diego is a cute puddycat and not a ferocious predator.

Some of the water effects, however, are less than convincing and the spectacular finale, with floodwaters racing through the valley, isn't remotely jaw-dropping.