The U.S.-Mexican production, which will open on more than 200 screens in Los Angeles and other cities on Wednesday, is the first Hispanic-centered movie that Fox Searchlight has distributed, reflecting the major studios' interest in tapping into a rapidly growing market. It stars Kate del Castillo as the mother, Rosario; Adrian Alonso as her son, Carlitos; and an eclectic supporting cast that includes America Ferrera of "Ugly Betty" as a child smuggler and the norteño supergroup Los Tigres del Norte as themselves.

But several of the film's most memorable characters are nameless illegal immigrants shown struggling to reach el norte or, once there, struggling to make ends meet financially and not be sent back to Mexico. Reading over the script during pre-production, Riggen "suddenly discovered that all these characters have one thing in common."

"All these people risked their lives crossing the border, leaving everything behind, for love," says Riggen, who was born and raised in Guadalajara, studied film at Columbia University and has lived in Los Angeles for the last several years. "For love of their families who they're going to go reach, for love of their families who they leave behind and send money to. But it always has to do with love and family."

A hot-button issue

Standing ovations at Rome and Toronto film festivals, along with mostly praise from critics, have greeted the movie so far. A "timely and energetic crowd-pleaser" was the Miami Herald's verdict, and the Hollywood Reporter opined that the film "overcomes its narrative shortcomings with a surfeit of heart."

Sweet-natured but tough-minded, "Under the Same Moon" arrives in theaters at a time when politicians, pundits and the public are engaging in (mainly) verbal slugfests over immigration, a recurrent hot-button issue in American history. But although Villalobos deliberately wove migrant-related themes into her screenplay, she agrees with Riggen that the movie is more of a personal than a political statement.

Specifically, Villalobos says, she wanted to explore the theme of abandoned children, a subject that became painfully real to her when her parents split up when she was 3 years old. For the next eight years she shuttled from Durango to Mexico City before settling with her mother in Utah when she was 11. She was the only Mexican in her new American school, and barely spoke a word of English.

"As an adult, there have been a lot of issues in my life as a result of feeling this kind of abandonment twice from both parents," Villalobos says. "And so that is actually what I wanted to explore, that sometimes parents feel like they're making the best decision for their children, and it may not necessarily be the case. So whether it's in the arms of strangers that happened during World War II, or whether it's through Operation Peter Pan, which is also what happened with a lot of the children — 14,000 children — in Cuba, or whether it's through these mothers and fathers that because of circumstances, financial circumstances, have to come and live in this country, these kids are left behind."

Villalobos wrote the first draft of the screenplay seven years ago, then shelved it while turning her attention to writing for television shows, including the animated Nickelodeon program "Go, Diego, Go!" along with other projects. Only years later did she realize that setting the story against the background of illegal immigration would allow her to "introduce the public to all of these people that are working in this country and see them as human beings instead of an issue."

Like Villalobos, the young hero of "Under the Same Moon," Carlitos, finds a way to push back against his parents' desertion. Tired of waiting for his absent mother to return to Mexico, he pays a pair of child smugglers to stow him away in their van and sneak him into the United States.

Once across the border, he falls in with a wild mix of humanity that includes many Mexican illegal immigrants, all struggling to keep their heads down and earn a few dollars washing dishes or picking tomatoes while steering clear of INS agents. All that Carlitos has to guide him in his search for Rosario is his mind's-eye vision of the Boyle Heights street corner — marked by a brightly colored mural — where his mother has been placing her long-distance calls to Mexico.

A perilous journey

Though "Under the Same Moon" is suitable for children, it doesn't shy from depicting the occasionally brutal obstacles that many poor, desperate Mexicans face in coming to look for work in the United States: dangerous river crossings, police raids and so on. Riggen brought a practiced social observer's eye to "Under the Same Moon": Her 2004 documentary "Family Portrait," which won the Jury Prize for short filmmaking at the Sundance Film Festival, was a nuanced look at the hardships of a poor Harlem family that legendary photographer Gordon Parks had profiled for Life magazine in 2068.

Riggen says that she tried to make her feature film debut "very realistic" but not necessarily bleak. "Under the Same Moon" shows some of the best and worst that people on both sides of the border are capable of, and nearly every character's motives are portrayed with understanding and compassion.

"I believe in goodness, I believe in humankind," Riggen says, "which I think makes me a little bit different than most of my colleague filmmakers in Mexico lately, which are usually seeing very obscure portraits of reality, very dark, the dark side of human beings. I didn't think this movie was like that at all. But of course we're not making a Disneyland film either. We're talking about a very important and cruel subject."

The key to making that cruel subject mesh with a heart-tugging family drama is Alonso's astonishingly assured performance. Riggen decided to audition the boy, who was turning 12 and had appeared in Luis Mandoki's "Innocent Voices" and played Joaquin in "The Legend of Zorro" with Antonio Banderas, after reading an interview he did with a Mexican magazine. She says that she cast him on the strength of his improvisational ability and his ease in handling vigorous exchanges with adult actors.

"This story was waiting for Adrian Alonso to be the right age to play the role," Villalobos says. "Because it is so difficult to find children not only that can act but can carry a movie. This kid is in this movie 90% of the film."

Shot mostly in and around Mexico City, on a budget of less than $2 million, the movie is one of only a handful of commercial films that have attempted to offer a transnational perspective on Mexican-American life. Funded in part by Mexico's national film commission, its performers include the well-known Mexican actors Eugenio Derbez and Carmen Salinas, as well as the voice of the popular L.A. radio show host Renán Almendárez Coello, better known as El Cucuy.

A marketing challenge

In one of the more head-scratching paradoxes of film marketing, Spanish-language movies tend to do badly with U.S. Hispanic audiences. Many industry followers believe this is because several acclaimed Spanish-language movies have been targeted not at Hispanics but at the urban art-house crowd. Also, some argue that the term "Hispanic" is far too broad and generic a category to encompass U.S. immigrants whose heritage may be Puerto Rican, Cuban, Dominican, Mexican or Central or South American.

"The size of the audience makes it an appealing target, and yet we've seen a lot of films come and go without reaching that target," says Nancy Utley, Fox Searchlight's chief operating officer. "I feel like some of the films were more artistic in nature and not mainstream, and others of them were trying to be pan-Latin and were not targeted enough at one of the Latin American groups."

Villalobos and Riggen say that the success of "Ugly Betty" and the "George Lopez" sitcom proves that there's a large potential audience for Hispanic-centric films and TV shows — provided they're well-told stories with broad appeal. "I think we have to stop thinking about making Hispanic films and make good movies," Riggen says.

As for the thornier social issues that "Under the Same Moon" raises, the women suggest there's an urgent need to move the discussion on illegal immigration beyond talk-radio ranting.

A number of critically favored films in recent years, including "Maria Full of Grace," "Quinceañera" and "Real Women Have Curves," have probed deeper into the nuances and challenges facing Mexican and Central and South American immigrants and their next-generation children.

"I think that the issue is being hijacked by a very small group of people," says Villalobos. "There are polls that are done on a regular basis about how Americans actually feel about the illegal immigrant issue. And most of the polls show that 60% to 65% of Americans believe that there should be a pathway to citizenship for illegal immigrants."

Now that she's living and working in Los Angeles, Riggen says she has realized there's a deep bond between the two countries and cultures. Like the bond between Rosario and her son, it's one that no mere wall can easily separate.

"I came to L.A. and I was very surprised and impressed by the fact that there is like an entire Mexican alternative city in the city," she says. "It's like two cities in one."