"Planet 51" is kids' stuff.

That's not a bad thing. Nor is it a great thing. It's just an observation that in many ways the movie is as old-school as the 1950s world it depicts.

Not our world, mind you. That's the premise of "Planet 51" — it begins by lightly veiling the fact that it takes place on another planet, billions of miles away from Earth. (And when I say lightly, don't worry — they get to it in the first minute or two.) Pre-Beatles rock, black-and-white TV and backyard cookouts are a staple of this world — as is a pop-culture obsession with alien invasion (another nod to the Earthly '50s).

Lem (voice of Justin Long) is a teen who's just gotten an underling's job at the local planetarium; suitably emboldened, he's even working on asking out the longtime object of his affections, Neera (Jessica Biel).

It's into this cozy little world that Capt. Charles T. "Chuck" Baker (Dwayne Johnson) lands. He's an American astronaut who thinks he's on a mindless mission (the type for which his intellect is well-suited) to get some rock samples from the presumably uninhabited planet, then switch on his spacecraft's autopilot and head for home as a conquering hero.

Oops.

Shoot-first Gen. Grawl (Gary Oldman) wants to find the uninvited visitor, whom he's certain means harm to the planet; so does Professor Kipple (John Cleese), who wants to remove his brain and study it. (It's nothing personal. He wants to remove everyone's brain).

Lem finds and befriends Chuck; he and pal Skiff (Seann William Scott) try to protect him from Grawl and Kipple and get him back on his ship. Along the way, Chuck teaches Lem a few life lessons about ... oh, the usual. How to meet girls, not be afraid of the unknown, that kind of thing. That last is a lesson a hawk like Grawl, who dislikes anyone and anything that is different (hmm, maybe there is a bit of a message here), needs to learn, as well.

In case you're worried about missing the point about how the Earthling is the alien here, there's an entire scene devoted to it.

Offering varying degrees of amusement along the way are lots of in-joke references to other movies, including "E.T.," "Star Wars," "Close Encounters of the Third Kind" and "WALL-E," the latter courtesy of Chuck's robot dog, Rover, who is obsessed with collecting rocks.

There are a few jokes for parents (including a variation on the ever-popular "how does he breathe through that thing"), but in this context they stand out.

This has been a great year for animated fare, with "Up" and the upcoming "Fantastic Mr. Fox" among the best movies, period.

"Planet 51" isn't as good as "Up" and "Fox." It doesn't try to be. And if you are 8 years old, you probably won't mind that a bit.