Brownsville Detective J.J. Treviño said police officers were called to the Southwest Key Casa Padre location after reports of a missing 15-year-old boy who ran away from the facility, the largest migrant children's center in the United States.

Jeff Eller, spokesman for the nonprofit Southwest Key Programs , which runs the facility, confirmed that a teenage boy left the center on Saturday and that facility officials called local law enforcement. An official with US Health & Human Services confirmed a boy ran away, but could not confirm what happened to him after that.

The 15-year old boy was an unaccompanied and undocumented minor; he had been under the care of the Southwest Key Programs facility for 36 days, a source familiar with the situation told CNN.

Before the child left the facility, authorities were in contact with an individual in Dallas who claimed to be the child's father, the source said. While attempting to reunite the child and "father," the source said it was discovered the man may not really have been the boy's biological father. While authorities were trying to determine the man's relationship to the boy, the 15-year-old left the facility.

Officers searched the surrounding area and waterways for the teen, but did not find him. Police have entered the boy's information into the missing children's database.

The "father" was informed the child left the care facility property, the source told CNN. On Sunday afternoon, the "father" said the 15-year-old called him and said he was back in Mexico after going across the river, the source told CNN. The child is getting money from his "father" to travel back to Honduras, the source said.

"I can tell you he's alive," the source said of the 15-year-old.

The child's father is in the United States and in the process of vetting to be a sponsor, another source familiar with the situation told CNN. Because this unaccompanied child ran away, if he is found, he will be returned to the custody of the Department of Homeland Security and re-referred to the Office of Refugee Resettlement, the source said.

The US Department of Health and Human Services does not identify unaccompanied children and "will not comment on specific cases," said a spokesperson with the Administration for Children and Families.

Staff at the Casa Padre facility are not allowed to restrain children if they decide to leave, the source said

Eller, the Southwest Key Programs spokesman, said the same thing. "As a licensed child care center, if a child attempts to leave any of our facilities, we cannot restrain them," he said. "We are not a detention center. We talk to them and try to get them to stay. If they leave the property, we call law enforcement."

As soon as children walk across the care facility property line, by law they become a missing child under the jurisdiction of the local police department, the source said. The source did not know if the children in the care facility are aware they can leave the facility at any time. When a child does leave, the Office of Refugee Resettlement is notified.

Over 19,000 children have been cared for by Southwest Key Programs this fiscal year and fewer than 50 children have chosen to leave the care centers alone, the source said.

Dr. Juan Sanchez, president and founder of Southwest Key Programs.

Juan Sanchez, the founder and president of Southwest Key Programs, said children at the shelter are able to call their families. Southwest Key Programs, as part of its intake process, works to find out how to get in touch with family members, Sanchez said. Parents held in Immigration and Customs Enforcement facilities may not have phone access or be reachable, he acknowledged, but he said that "a majority of separated children have other family here they can call."

The Casa Padre shelter opened last year. Southwest Key Programs, which has operated immigrant children's shelters since 1997, operates 26 other shelters in Texas, Arizona and California. Aside form undocumented children, the nonprofit also handles other children and has received more than $807 million in federal grants over the past three fiscal years for services for immigrant children.