Felipe and his father were detained by immigration authorities on Dec. 18, the report said.

Days later, on Dec. 24, a border patrol agent “noticed that the child appeared ill and interviewed the father, who requested medical treatment for his son,” the report said.

The boy was taken to a nearby hospital, where he was found to have an upper respiratory infection, and was “prescribed amoxicillin and acetaminophen.” The hospital staff then “discharged the child, who was returned to the U.S.B.P. facility.”

The authorities obtained and administered the boy’s medicine once he was back at the border patrol facility, the inspector general’s report said, and the boy “improved briefly, and subsequently worsened.”

For the second time, the boy was taken to the hospital.

“Upon arrival, the child was unresponsive and pronounced dead,” the report said, which states that the cause of death was “sepsis caused by Staphylococcus aureus bacteria.” An autopsy report for Felipe, who died on Dec. 24, also mentioned complications from the flu as a cause of death.

It was not immediately clear why the flu was not listed in the inspector general’s report.

Representative Joaquin Castro of Texas, the chairman of the Congressional Hispanic Caucus, said in a statement late Friday that the inspector general’s investigations “leave many questions, and I will request a meeting as soon as possible to get answers.”

“I went to Antelope Wells and Alamogordo to investigate the deaths of Felipe and Jakelin, and I was startled by the conditions and lack of even the most basic medical facilities,’’ he continued. “The bottom line is that migrant children are being treated with less than basic humane care at our border and are dying as a result. In fact, more children have died in C.B.P. custody since the deaths of Jakelin and Felipe. This pattern of death should disturb and alarm us all.”

In February, caucus members introduced legislation directing Customs and Border Protection to implement a set of minimum humanitarian standards for the treatment of people in the agency’s custody.