context: The film tells the story of Rosario (Kate del Castillo), a mother who illegally immigrates to the United States, and her nine-year-old son, Carlitos (AdriÃ¡n Alonso). Rosario and Carlitos have not seen each other in four years, since Carlitos was five. Rosario, now living in Los Angeles, California, calls her son (who is still in Mexico) every Sunday at 10 A.M. from a payphone. Carlitos lives in a small Mexican village with his ill grandmother and his repressive aunt and uncle, who try to take custody of him in order to get the money that Rosario sends to him. One day, while working for a woman named Carmen (Carmen Salinas), Carlitos encounters two American immigrant transporters (coyotes), Martha (America Ferrera) and David (Jesse Garcia), who offer to smuggle small children across the border.
  When his grandmother passes away, Carlitos decides that he cannot live with his aunt and uncle, so he finds the two coyotes. Though he successfully crosses the border without being caught, the car that he hides in is towed away and he is separated from the two coyotes since they had parking violations and expired tags and didn't pay for them. Afterwards, Carlitos continues the journey, eventually staying with other undocumented immigrants while they pick tomatoes. However, immigration police raid the building, and arrest most of the workers, but Carlitos and another worker named Enrique (Eugenio Derbez), who does not like Carlitos, escape.
  While traveling, Carlitos and Enrique arrive at a restaurant managed by a Native American man and his wife. Carlitos manages to gain employment for both Enrique and himself. At the restaurant, Carlitos looks up his absentee father, Oscar Aguilar Pons (Ernesto D'Alessio), who he learned about from his aunt and uncle despite his grandmother's wishes, in a phone book, and they meet at a wholesale store and have lunch there. Oscar agrees to take Carlitos to Los Angeles where Rosario is, but later changes his mind, angering Carlitos.
  In turn, Enrique decides to take Carlitos to Los Angeles. The two take a bus ride and make it to LA. Carmen manages a phone call to Rosario to let her know that Carlitos is missing and Rosario decides to leave on a bus back to Mexico. Meanwhile, Carlitos and Enrique searched the city for the pay-phone that his mother called him from every Sunday. Failing to find the pay-phone after hours, the two fall asleep on a park bench. As Rosario is about to depart on a bus ride, seeing a pay-phone by the bus reminds her of Carlitos and she gathers her thoughts to make a decision.
  As the sun rises, Carlitos is still sleeping on a park bench, Enrique leaves to buy food and Carlitos is spotted by the police. Carlitos is almost caught by the police, but Enrique throws a cup of coffee at the officers, provoking the officers to chase him instead. Carlitos manages to escape but Enrique is caught. He finds himself in a familiar place that matched all of his mother's descriptions and sees her across the street waiting at a payphone. Carlitos calls out to her and she is overjoyed to see that he is unharmed. There are too many cars for Carlitos to cross against the light, so the two anxiously wait on either side of the street. The movie ends with the 'walk' sign between the two turning on.
question: Why must Carlito cross the border?
answer: two coyotes