Despite a title that sounds a bit like a visit to grandma’s house gone awry, “The Last Mimzy” has a promising premise and more than its share of engaging moments. But uneven direction and poorly developed plot additions undermine the final product.

New Line Cinema chairman Robert Shaye often makes good use of the cinematic tricks at his disposal, but he’s clearly a newcomer to the director’s chair; sometimes he is able to coax inspired performances, but at others he leaves his actors to languish. Similarly, the cinematography often gives “Mimzy” the feel of an after-school special.

Based on a 1943 short story by Lewis Padgett (the pen name of Henry Kuttner and his wife, C. L. Moore), “The Last Mimzy” follows two young siblings who discover a box full of toys from the future. As Noah (Chris O’Neil) and Emma (Rhiannon Leigh Wryn) begin to play with them, their intelligence levels correspondingly skyrocket. One of the toys, a stuffed bunny named Mimzy, communicates with Emma, explaining that they are from the future and need the children’s help to save mankind. As Noah and Emma try to help, they must compete against time and adults, who cannot comprehend the knowledge the children have acquired.

Padgett’s story, “Mimsy Were the Borogoves,” smartly exploited the difference in intellectual development between children and adults to explain why someone from the future might seek the aid of the young over that of the old. Unconstrained by the rules of logic that come with age, children are more open to the vastly complex learning structures of this future world. The author also tied his wormhole theory to Lewis Carroll’s poem “Jabberwocky,” showing that other attempts at time travel had been made from the future.

But where Padgett left much of the story open to the imagination, “The Last Mimzy” tries a bit too hard to fill in the details. Updating the story to the present day, the film makes some smart connections to video games and even involves Homeland Security. For the younger ones in the audience, the toys should capture and thrill the imaginations. Computer-generated effects and unexpected morphing give the toys a lifelike quality, and the film makes good use of it. But other effects are less successful, like the silly noise Noah is forced to make to communicate with spiders and scenes from the future, which make the rescued world look like an ad for women’s deodorant.

The moral ambiguity of the toys is an interesting element in the film, but it is dealt with superficially. Ultimately, the outcome of the events is predetermined by the genre of the film. If “Mimzy” were a horror film, the onscreen parents would be saps for following along so placidly. Similarly, the involvement of Homeland Security, though clever in concept, eventually becomes unnecessary. At one point, Seattle’s top Homeland Security agent is baffled by the strange events he has witnessed and even turns to the family to say: “I don’t understand this, but I know I’m sorry. Is there anything I can do for you guys?”

Mr. Shaye hurts the film by creating some small moments in exquisite detail and rushing past others. Watching Noah transform from an average, discouraged student to an active thinker is a great step that the parents and the children in the theater can enjoy equally. The scenes in which the toys fascinate and teach the siblings are an achievement and both Mr. O’Neil and Miss Wryn often exhibit convincing talents. But at other times they are exceedingly flat, dropping the momentum of the story. The adults fare no better. Joely Richardson does a capable job as their mother, but she is left on the sidelines, confused or outraged, for much of the plot. Timothy Hutton does is a predictably doting father, but it is depressing to see how well he has aged into that role.

Rainn Wilson, as the quirky science teacher, is the only adult given room to move, and he brings the same distinguishable charms that he utilizes in his roles on NBC’s “The Office.” Kathryn Hahn, however, does not fare as well as his lottery-obsessed new age girlfriend.

It is apparent that “The Last Mimzy” would like to be considered among age-defining sci-fi films like “E.T.” and “Close Encounters of the Third Kind,” but it is ultimately grounded by its leaden attempts to enhance Padgett’s story. Efforts to explain the mechanics of time travel and why the future has sent these toys back to the future are surprisingly lackluster, and by the time the dynamics are fully explained, it’s a bit of a wonder why anyone would need a mimzy at all.

mkeane@nysun.com