U.S. Customs and Border Protection announced changes to the way it handles child migrants in custody on Tuesday after an 8-year-old Guatemalan boy died of unknown causes on Christmas Eve in New Mexico.

It was the second death of a child in the agency's care this month.

Jakelin Caal Maquin, 7, also of Guatemala, died in custody after traveling to the U.S. with a group of 163 people. Her body arrived in Guatemala on Monday.

The coffin of Jakelin Caal is carried to a cemetery in her native Guatemala on Tuesday. Jakelin, 7, died in a Texas hospital two days after being taken into custody by U.S. Border Patrol agents in a remote stretch of the New Mexico desert. JOHAN ORDONEZ / AFP - Getty Images

After the 8-year-old boy’s death, the agency said in a statement late Tuesday that Border Patrol would now conduct “secondary medical checks” on all children in custody, with a focus on children under the age of 10. It was not clear from the statement how and where those checks would be conducted.

It is considering requesting additional medical assistance from other agencies — including Health and Human Services and the Department of Defense — and coordinating with the Centers for Disease Control and Prevention on the numbers of children in custody, the statement said.

The agency said it is also reviewing how it holds immigrants in custody so it can relieve problems with capacity in its centers in the El Paso, Texas, area.

With border crossings surging, CBP processes thousands of children — both alone and with their parents — every month.

The federal government is currently partially shut down because of a dispute between President Donald Trump and Congress over his demand for a border wall. Trump dug in on the issue Tuesday, telling reporters that the U.S. must have "a wall, a fence, whatever they'd like to call it."

He also insisted that the wall — through renovations and new contracts — is actually already scheduled to be built and refurbished. He claimed that 115 miles of wall was set to be constructed in Texas, and that he would visit the border at the end of January for a groundbreaking ceremony.

Rep. Joaquin Castro, D-Texas, identified the boy who died on Christmas Eve as Felipe Alonzo-Gomez. He was first taken into custody with his father 3 miles outside of El Paso on Dec. 18, according to the CBP statement, which included a timeline of the child’s last day in custody.

Castro, the incoming chairman of the Congressional Hispanic Caucus, credited CBP for its timely public notification but also blamed the Trump administration's broader immigration policy for putting migrants in harm's way.

"The Administration’s policy of turning people away from legal ports of entry, otherwise known as metering, is putting families and children in great danger," Castro said in a statement.

The official cause of the child's death is still unknown and the CBP's Office of Professional Responsibility will conduct a review, consistent with policy, according to the statement.

According to the CBP timeline given in the statement late Tuesday night, the boy and his father were given food, water, juice and showers throughout their time in the United States. Agents also performed regular “welfare checks” to check that they were safe and secure.

At 9 a.m. local time on Dec. 24, a processing agent noticed that Felipe “was coughing and appeared to have glossy eyes.” He was sent to a medical center not long after where he was examined, given tests for strep and told he had a common cold.

During an evaluation for release at 1:20 p.m., he had a fever of 103 degrees and was held for further evaluation for another hour and a half. He was then released with a prescription for amoxicillin and ibuprofen.

After returning to the holding center, the father and son were given a hot meal and the boy received a dose of his medication. Later on, the father declined further medical assistance saying that his son had been feeling better.

At 10 p.m., agents sent the child back to the same hospital after he appeared nauseated and sluggish. He lost consciousness on the way and hospital staff were unable to resuscitate him. He was pronounced dead at 11:48 p.m. on Christmas Eve.

The father, who is still in custody, spoke with his spouse in Guatemala and the Guatemalan Consulate, according to the statement. The child’s body will be sent to Albuquerque for autopsy and then to the Alamogordo Funeral Home.

The American Civil Liberties Union said in a tweet Tuesday that the boy's death was "a horrific tragedy" and that CBP should be held accountable. The group called for the incoming Congress to investigate the Department of Homeland Security, which includes CBP.

Customs and Border Protection Commissioner Kevin K. McAleenan called the death a “tragic loss,” and said “our deepest sympathies go out to the family.”

CBP announced last week that it would begin informing Congress and the media within 24 hours after someone dies in its custody.

In testimony before the Senate Judiciary Committee on Dec. 11, McAleenan told the senators that CBP's facilities were built to handle “mostly male, single adults in custody, not families or children.”

“I want to make sure that we have the capability to care for children in our custody with the right medical and mental health professionals and that we have the partnership with Health and Human Services to expeditiously transfer children to a more appropriate custody situation," he said.

As parts of the border have been fortified with fencing and other barriers over the years, migrants and smugglers have sought other entry points, moving to more treacherous parts of the nearly 2,000-mile United States-Mexico boundary.

CORRECTION (Dec. 26, 2018, 3:08 p.m. ET): An earlier version of this article misstated the first name of the Guatemalan boy who died while in the custody of the U.S. Customs and Border Protection. He is Felipe Alonzo-Gomez, not Felix.