Menno Meyjes’ film is destined to be dismissed as “K-PAX” with a kid, and while that’s not exactly accurate from the narrative perspective, in terms of quality it’s pretty apt. “The Martian Child” is an inspirational weepie about a widower who adopts a psychologically damaged young orphan, abandoned by his mother, who claims to be a visitor from the Red Planet studying human society. Unlike in the Kevin Spacey movie, there’s no doubt about whether the kid’s from another planet or not—the pose is obviously the psychological defense mechanism of a damaged child. But the degree of manipulation is no less in this case.

John Cusack, working with Meyjes a second time after the decidedly oddball young Hitler film “Max” (2002), stars as David, a hot-ticket fantasy writer who’s still grieving over the death of his wife after two years. He tries to break through the emotional wall by considering adopting Dennis (Bobby Coleman), a withdrawn little boy who claims to be a Martian and spends most of his time at the orphanage run by supportive Sophie (Sophie Okonedo) in a cardboard box to protect himself from the sun’s harmful rays. David has doubts about adopting at all, but he’s drawn to the troubled lad, drawing him out of his box with sunglasses and sunscreen and eventually taking him home “on audition,” as it were.

From here the story goes where you’d expect. The two bond—after all, David creates a fantasy world in his books, too—by gradually respecting each other’s eccentricities. There’s a skeptical child welfare official (Richard Schiff) who keeps close tabs on the duo and threatens to revoke the adoption if the child doesn’t acclimate sufficiently to the real world. And there are schoolteachers who demonstrate little compassion for the boy. (By contrast, the psychologist played by veteran Howard Hesseman is so nonchalant about Dennis’ case, not even bothering to schedule follow-up sessions, that he should have his license revoked.) David’s homemaker sister Liz (Joan Cusack, playing essentially the same part she did in 2004’s equally saccharine “Raising Helen”) provides the sarcastic voice of realism, expressing practical doubts about David becoming a dad but proving helpful as needed. The new domestic arrangement affects David’s writing—a problem, since he’s under contract to provide a new sci-fi book to his demanding publisher (Anjelica Huston), as his anxious agent (Oliver Platt) reminds him. And, of course, there’s a beautiful friend, Harlee (Amanda Peet), who encourages the bond between David and Dennis and serves as the obligatory romantic interest for the widower and new father.

But as by-the-numbers as most of the movie is, it’s the last act that takes things to ludicrous extremes. A search for the boy, who’s predictably run away after an unpleasant confrontation, winds up—if you can believe it—on a building ledge. (Don’t worry, nobody falls.) And just to make sure we know how to react to it, Meyjes inserts a shot of characters hugging and crying the way viewers are supposed to. But even this is topped by the twist involving David’s book, which turns out to be not the continuation of his best-selling series that his publisher demands but…you guessed it, an autobiographical memoir (a reflection of the David Gerrold novel from which the script was adapted).

“The Martian Child” may mean well, but it’s incredibly cloying, and the cast fall into the patterns the story demands. Cusack mopes about tiresomely—he needs to start choosing better material—while Peet, Platt, Okonedo, Joan Cusack, Huston and especially Schiff can’t get past stereotype. The best performance, in fact, comes from Coleman, who’s actually rather endearing, but his shoulders are too small to carry things alone. Technically the film is competently made but unexceptional.

Ultimately, though, “The Martian Child” is hobbled by its ham-fisted effort to strum our heartstrings. The movie may want to convey a message about human emotion, but narratively it’s actually so far out in terms of credulity that it might as well have come from another planet itself.