Sid the Sloth (voiced by John Leguizamo) and Manny the Mammoth (Romano) find a young human baby abandoned after its mother is attacked by a group of sabre-toothed tigers. They team up (somewhat reluctantly) to bring the baby back to its family. They are joined along the way by Diego (Leary), a sabre-toothed tiger with his own agenda.
Ice Age is no Shrek. It tries hard to be, but it doesn't have the depth. The story is told well enough, though, and the animation is great. In particular, the three leads have an uncanny resemblance to their respective voice actors, which helps trick you into thinking that they're real. And the individual sequences are well put together, and quite funny. The Dodo sequence is a standout. Somehow, though, all the parts don't come together at the end of the day. I'd certainly recommend watching it, just don't expect the same quality as Shrek or most films from Pixar.

Jimmy has friends of merely human intelligence, a laboratory full of space-age experimental projects, and a robot dog that can explode and reassemble on command. Unfortunately, he also has given little thought to the results of sending out invitations, with directions, to extraterrestrial intelligences. Having launched his backyard satellite and told them to come on in, Jimmy finds that the Yokians' visit to his home town, Retroville, is more than he had had in mind.
The Yokians capture every adult on the planet and take them home to stock up for the lean season. This means that all the kids have no limits on junk food and staying up late - but after a weekend of this, they want their parents back. Jimmy therefore creates a space armada from amusement rides, and off he and his fellow fledgelings blast to rescue the adults.
Kids will love this film and then never think about it again unless it's handy on video. The film isn't just for kids, though. There are enjoyable allusions to The Blair Witch Project, Star Wars, and Star Trek, and a few jokes just for adults. The animation is intentionally retro. By the way, Jean-Luc Picard himself provides the voice for King Goobot, leader of the Yokians.