Sonia Nazario, the writer, found Enrique in Nuevo Laredo, Mexico, in May 2000. She and Don Bartletti, the photographer, spent two weeks with him there and rejoined him at the end of his journey in North Carolina. Then, based on Nazario's extensive interviews with him in Mexico and during three visits to North Carolina, she and Bartletti retraced each step Enrique had taken, beginning at his home in Honduras.

Between May and September 2000, Nazario and Bartletti spent three months working their way north through Mexico just as Enrique had, riding the tops of seven freight trains and interviewing and photographing people Enrique had encountered, along with dozens of other children and adults making the same journey. Nazario and Bartletti walked around immigration checkpoints and hitchhiked with truckers, exactly as Enrique had. To retrace Enrique's steps, they traversed 13 of Mexico's 31 states.

Nazario conducted interviews in the United States, Honduras, Mexico and Guatemala with immigrant rights advocates, shelter workers, academics, medical workers, government officials, police officers and priests and nuns who minister to immigrants. At four INS detention centers in California and Texas and in two shelters for child migrants in Tijuana and Mexicali, Mexico, she interviewed youngsters who had made their way north on top of freight trains. She also consulted academic studies and books about immigration.

The Los Angeles Times has a strong preference for naming the subjects of its articles in full. It has done so with two members of Enrique's family, his girlfriend and a friend. But The Times has decided to identify Enrique, his mother, father and two sisters by publishing only their first names and to withhold the maternal or paternal name, or both, of six relatives as well as some details of Enrique's employment. A database review by Times researcher Nona Yates showed that publishing their full names would make Enrique readily identifiable to authorities. In 1998, the Raleigh, N.C., News and Observer profiled an illegal immigrant whom it fully identified by name and workplace. Authorities arrested the subject of the profile, four co-workers and a customer for being undocumented immigrants. The Times' decision in this instance is intended to allow Enrique and his family to live their lives as they would have had they not provided information for this story.

Scenes from Enrique's life in Honduras with his mother and sister, including his mother's departure: written from interviews with Enrique; his mother, Lourdes; his aunts Mirian Liliana Aguilera and Rosa Amalia; his maternal grandmother, Agueda Amalia Valladares; and his mother's cousin Maria Edelmira Sanchez Mejia. Quotation in which Enrique asks his mother to look at things: from Lourdes and Maria Edelmira.

Lourdes' departing words to Enrique: from Lourdes and Enrique.

Enrique's reaction to his mother's departure: from his paternal grandmother, Maria Marcos. The boy's remarks asking about his mother come from Marcos.

Estimate that at least 48,000 children enter the United States from Central America and Mexico each year, illegally and without either parent: This total, for 2001, is reached by adding the following numbers, which are the latest available. The U.S. Immigration and Naturalization Service says it detained 2,401 Central American children. The INS has no figure for Mexican children, but Mexico's Ministry of Foreign Affairs says the INS detained 12,019 of them. Scholars, including Robert Bach, former INS executive associate commissioner for policy, planning and programs, estimate that about 33,600 children are not caught.

For 2000, the total was 59,000.

Reasons children travel to the United States and information that many come in search of their mothers: from Roy de la Cerda Jr., the lead counselor at International Educational Services Inc., an INS-contracted detention shelter for unaccompanied minors in Los Fresnos, Texas. His information is corroborated by Aldo Pumariega, principal at the Bellagio Road Newcomer School; Bradley Pilon, a psychologist who counsels immigrant students in the Los Angeles Unified School District; and Rafael Martinez, director of Casa YMCA, an immigrant shelter in Piedras Negras, Mexico.

Children bringing photos of themselves in mothers' arms: from Ralph Morales, pastor of the End of the Road ministry in Harlingen, Texas.

Estimate that half of Central American children ride trains without smugglers: from Haydee Sanchez, executive director of Youth Empowerment Services, a nonprofit Los Angeles group that helps immigrants; Olga Cantarero, a coordinator for the nonprofit Casa de Proyecto Libertad in Harlingen, Texas, which provides legal help to INS child detainees; and De la Cerda.

Details about travel through Mexico: from immigrant children in Mexico and the United States and from children in INS detention facilities in Texas and California. Included are Nazario's observations as she traveled with children on Mexican freight trains. The University of Houston study about violence to children is titled "Potentially Traumatic Events Among Unaccompanied Migrant Children From Central America" and was published in 1997.

Encountering children as young as 7: from Pedro Mendoza Garcia, a railroad security guard at a depot near Nuevo Laredo. Remarks of 9-year-old boy searching for his mother who is in San Francisco: from Haydee Sanchez in Los Angeles. Police placed him in her care until she found his mother.

Typical age of children: from INS data and immigrant shelter workers in Mexico.

How children recall their mothers: from interviews with several of them, including Ermis Galeano, 16, and Mery Gabriela Posas Izaguirre, 15, questioned in Mexico on their way to find their mothers in the United States.

Enrique's life with his father: from interviews with Enrique; his paternal grandmother, Maria; his father, Luis; and his stepmother, Suyapa Alvarez. Enrique's question about his mother's coming for him: from Maria.

Lourdes' journey and her early years as an immigrant: from her and members of her family. Lourdes' remark about feeding another child: from Lourdes. Grandmother Maria's assurance that Lourdes would be home soon: from Maria, confirmed by Enrique.

Enrique's father's new family and how he left Enrique: from Enrique, his father and his grandmother Maria. Enrique's statement to his sister Belky about how his father did not love him anymore: from Belky and Enrique. Maria said Enrique said the same words to her.

Belky's reaction to Mother's Day and her mother's absence: from interviews with Lourdes, Enrique, Belky and his aunt Rosa Amalia. Belky's commiseration with a friend whose mother left her behind: from Belky.