An 8-year-old Guatemalan migrant boy died early on Christmas Day after being detained by U.S. border agents, the U.S. Customs and Border Protection (CBP) said, the second migrant child to die in U.S. detention this month.

The boy and his father were in CBP custody on Monday when a Border Patrol agent noticed the child showing signs of illness, CBP said in a statement. The father and son were taken to the Gerald Champion Regional Medical Center in Alamogordo, New Mexico, where the boy was diagnosed with a common cold and fever, and eventually released by hospital staff, but later that evening, the boy began vomiting and was transferred back to the hospital. He died there early on Tuesday, CBP said, adding that the official cause of death was not known.

The boy’s death followed the death in early December of 7-year-old Jakelin Caal, also from Guatemala. She died after being detained along with her father by U.S. border agents in a remote part of New Mexico.

After the second death, the CBP announced it was developing several policy changes late Tuesday.

It will conduct secondary medical checks on all children in its custody, with a focus on those under 10, the agency said in a release.

The agency will also work with Immigration and Customs Enforcement to improve custody options, such as better transportation to Family Residential Centers and supervised release, and working with non-governmental agencies for housing.

The boy and his father entered the United States via El Paso, Texas, on Dec. 18 and were transferred to a border patrol station in Alamogordo on Dec. 23.