Story highlights A Mexican family who entered the U.S. illegally tells how they have now fled the U.S.

Two children, who were born in the U.S., are struggling to learn in Spanish classrooms

One says he misses the books available in Arizona; the other misses parks and big houses

The parents say they left the U.S. feeling persecuted by Arizona's new immigration laws

In a remote town in northern Mexico, a 10-year-old-boy is struggling with his homework. His name is Oscar Castellanos, and the fifth-grader is getting extra help from his father because he's having trouble adjusting to his new school.

The student enrolled at Leona Vicario Elementary in the town of Cananea is technically a foreigner in his father's land. Oscar was born in Arizona and is a U.S. citizen. He recites the U.S. Pledge of Allegiance by memory without hesitation. His English accent is that of a boy raised in the American Southwest.

Oscar's family moved back to Mexico after the state of Arizona approved some of the toughest immigration laws in the United States. Now they live in Cananea, a mining town of 30,000, about 35 miles south of the U.S.-Mexico border.

When asked whether it's been difficult to adjust to life in Mexico, his answer is "kind of." Pressed to elaborate, he adds that one of his main challenges is having "to speak another language."

Oscar says he misses the abundance of books available to him in U.S. schools. In Mexico, textbooks are free, but finding additional reading material is often a challenge, especially in a provincial town that's a 23-hour drive from Mexico City.

Oscar's 6-year-old sister, Angie, also is an American citizen. Just like her brother, she was born in Tucson, the second largest city in Arizona, with a population of just over a half a million people.

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When asked about the things she misses about the United States, she mentions "the stores, bigger houses and parks."

The children's parents, Oscar and Maria Castellanos, lived in Arizona for 13 years as undocumented immigrants, doing all kinds of odd jobs to survive and provide for their children. They had managed to buy a house and a car when the law, known as SB1070, was passed in April 2010.

The state law originally authorized police to arrest undocumented immigrants without warrant, if there were probable cause to believe that they had committed offenses that could lead to their deportation. It made being in Arizona without immigration or government identification documents a state crime. And it banned unauthorized immigrants from seeking work.

The U.S. Supreme Court struck down those provisions in June but let stand a further clause that allows police to check a person's immigration status while enforcing other laws, but by then, the Castellanoses had gone.

Maria, 44, says they finally made the decision to return to their country to protect their mental sanity. "We would feel persecuted and harassed. We felt bad. It was nerve-wracking, especially when we had to go outside to go to work."

For Oscar, 41, the most difficult part was to abandon everything they had worked so long to build. They left their three-bedroom house and sold their Volkswagen Touareg SUV.

Now they live in a two-bedroom house and drive a Tsuru, an economy Nissan sedan not sold in the United States. "It was difficult, because we had everything there. We had to leave everything behind and return to Mexico. It was difficult," Oscar says.

Oscar Castellanos says they endured years of living in fear in the U.S. but also hoped they were building a better life for their children.

It's nearly impossible to estimate how many Mexican immigrants went back home after states like Alabama and Georgia also pushed legislation to crack down on illegal immigration, following in Arizona's footsteps.

According to the Pew Hispanic Center, net migration from Mexico to the United States fell to zero or less from 2005 to 2010.

This means the number of immigrants entering the United States is likely equal or smaller than the number leaving, although, the study adds, some left the U.S. unwillingly: They were deported.

In Mexico, Angie Castellanos sings her ABCs in English to her family. She has yet to learn them in Spanish.

The Castellanos family is among the fortunate ones. Oscar was able to find a job as a miner just a few months after returning to his hometown in northern Mexico. Maria is managing a restaurant, and both kids are enrolled in school.

Maria has been helping Angie with her Spanish while Oscar teaches math to his son.

Both parents say they try not to think about what might have been, while the children frequently seem to miss the life they had across the border.