Anyone wanting to understand how good “Rango” is need only pay a visit to “Mars Needs Mom,” the new exercise in stop-motion animation from Robert Zemeckis and his crew. Visually the adaptation of Berkeley Breathed’s children’s book is impressive, an advance on “The Polar Express” and even the more recent “A Christmas Carol,” though the facial expressiveness of the human characters is still in need of improvement. But in narrative terms it’s not much better than standard TV fare.

The pint-sized hero is Milo (“acted” by Seth Green and voiced by Seth Dusky), a kid who resists the efforts of his loving mother (Joan Cusack) to get him to do his chores and eat his broccoli. Unbeknownst to either of them, they’re being watched from Mars, where the stern old supervisor (Mindy Sterling) of what amounts to a totalitarian feminist regime is searching for an earth mom with the proper maternal instincts to kidnap and provide the template for a new generation of nanny-bots that will raise the coming crop of female hatchlings (male ones are simply tossed into the wild to fend for themselves). And Milo’s mom is the hag’s choice; she’s abducted just after the kid has blurted out that he wished he didn’t have a mother, hurting her feelings. Needless to say, he stows away on the Martian spaceship to rescue her and bring her home.

What follows is basically a protracted chase that might be described as a cross between the second half of “Wall-E” and the recent sequel to “Tron.” Milo’s assisted by an older earth refugee, Gribble (Dan Fogler), who’s been on the Red Planet for years and is still a big kid at heart, and Ki (Elizabeth Harnois), a Martian girl in rebellion against the bland, colorless system the supervisor has created. It’s not spoiling much to reveal that not only does Milo succeed in getting his mom back, but the threesome also engineer the downfall of the cruel Martian matriarchy and the restoration of a true familial ethos there.

This is kind of a weird scenario for a kiddie movie in any event, based as it is on the premise of potential loss of a parent—a prospect any child would find disturbing. (Just think how many toddlers have been traumatized by “Bambi” over the years.) But it’s not particularly well executed, either. Technically it’s fine, though not outstanding (the wide-screen images are impressive, and the obligatory 3D effects are okay, though as noted above the plastic-looking faces are a minus).

But there’s little wit in the dialogue. Milo comes across as just a standard-issue Saturday morning-cartoon kid, and while Ki’s habit of talking in ‘70s-style patois she’s learned from old flower-power earth sitcoms is good for a few laughs, Gribble, who’s supposed to be the comic sparkplug, is more obnoxious than endearing. Partially that’s because he’s voiced by Fogler, who’s being advertised as a young comic genius in the Belushi mold but thus far seems to bring little to the table but an abrasive sort of manic energy. Cusack, meanwhile, is simply wasted, and Tom Everett Scott is appropriately bland in the cipher part of the mostly-absent father figure.

The result is one of those mediocre computer-animated kidflicks that seem to come along every couple of weeks nowadays. Mars may need moms, but the movie desperately needs more imagination, charm and heart.