It’s not hard to see why “Under the Same Moon” (“La Misma luna”) received a standing ovation at the 2007 Sundance Film Festival. It contains basically everything that would appeal to your average guilt-ridden liberal: lots of ethnic flavor, bad white people, hard-working Mexicans, and an adorable kid who embodies everything good about (illegal) immigrant heroism. Overall, “Under the Same Moon” is watchable, entertaining, and well-meaning, but the predictable plot fails to address immigration as a complex social issue.

The movie follows nine-year-old Carlitos (played with sweet seriousness by Adrian Alfonso) as he crosses the Mexican-American border illegally after his grandmother’s death to search for his mother. The plot is conventional, but Carlitos is heartbreakingly cute. His relationship with Enrique (Eugenio Derbez), the migrant worker who comes to take care of him, is charming, funny, and by far the film’s greatest strength.

Like nearly all movies with a political agenda, however, “Under the Same Moon” has its limitations. Director Patricia Riggen primarily uses the mother-son story to frame a broad survey of illegal immigrant hardship. It’s a well-intentioned move to educate the public, but the film’s sweeping view of Mexican working life gives us a simplified picture of saintly illegals that sometimes veers a bit too close to propaganda.

Over the course of several days, Carlitos somehow manages to see first-hand all aspects of the Mexican illegal experience: he picks tomatoes with the migrant workers, washes dishes in a restaurant, gets chased by the cops, and even has a run-in with a nasty white drug addict. In a parallel plot, his mother Rosario (Kate del Castillo) toils at the houses of her rich white employers, loses one of her crucial jobs, and searches in vain for another one.

In the meantime, we learn all sorts of facts about illegals, like how they use P.O. boxes for their mail (“so the INS can’t find them,” as Enrique explains). We’re even introduced to poor Mexican-American college students Marta and David (played by America Ferrera of “Ugly Betty” fame and Jesse Garcia from “Quinceaña”) who resort to taking illegals across the border for tuition money.

It’s a credit to the filmmakers that the movie’s didacticism doesn’t feel unbearably contrived while it’s happening. The depiction of Mexican life, on both sides of the border, is rich and spirited, saving the movie from the danger of being too dour about its characters’ hardships. Carlitos’ journey progresses with adequate believability, and the minor Mexican characters that move in and out of Carlitos’ life are, realistically, good-hearted enough to be trusted.

But then the Big Message awkwardly forces its way into the movie. When David is hesitant to smuggle Carlitos across the border, Marta asks, “Do you want to drop out of school or do you want to get the money?” A clip of Spanish-language radio in the movie even directly criticizes California governor Arnold Schwarzenegger’s refusal to sign a pro-immigrant bill, which, as the radio announcer sneers, “makes him a jerk.”

When Enrique explains the illegal immigrant lifestyle to Carlitos, he says, “No one chooses to live this way unless they have a reason.” This statement describes equally well the motivations of the characters and of the film itself: no one would make a movie like this without a major political point. Luckily for “Under the Same Moon,” Carlitos and Enrique are charming enough to make it watchable.