A 15-year-old boy ran away from a Texas shelter for migrant children, police said Sunday. The boy is now in Mexico, according to a source with direct knowledge of the incident.

The boy ran from Casa Padre, a child care facility in Brownsville, on Saturday, and was in conversations to be reunited with a man whom he called his father, the source said.

Details about the man, such as if he had already been living in the United States and for how long, weren't immediately clear. There had been a discrepancy in a DNA test, and before they could be sorted out, the child ran away, according to the source.

The source said that the boy is in Mexico and that the man whom he calls his father is sending him money to get him back to Honduras.

Brownsville police said the received a call at around 4:30 p.m. (5:30 p.m. ET) Saturday that a 15-year-old boy had run away from the shelter. Search teams were called out, including a boat to search a nearby pond, but the child wasn't found, said Jose Treviño, a police spokesman.

Southwest Key confirmed in a statement that a boy left the facility on Saturday.

"As a licensed child care center, if a child attempts to leave any of our facilities, we cannot restrain them," the statement 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."

Occupants at Casa Padre, an immigrant shelter for unaccompanied minors, in Brownsville, Texas, in a photo provided by the Department of Health and Human Services on June 14. U.S. Department of Health and Human Services via Reuters

The source with knowledge of the incident said Southwest Key has 19,849 children in its care, 42 of whom have left.

Earlier this month, NBC News was among the first news organizations granted access to the facility, where children — both those who were separated from their parents and those who came to the United States on their own — spend 22 hours a day during the week.

The facility, a former Walmart store, houses nearly 1,500 boys ages 10 to 17.