Democratic lawmakers on Wednesday called for congressional hearings after the deaths of two migrant children in U.S. custody in one month and said they were working to draft legislation requiring health standards for immigration agencies.

“We believe there should be a congressional investigation as soon as Congress comes back into session,” Rep. Joaquín Castro, D-Tex., the incoming chairman of the Congressional Hispanic Caucus, said on a call with reporters Wednesday afternoon. He added that "systemic failures" at immigration agencies were contributing "to serious injury and illness and to the deaths of these migrants."

Rep. Raul Ruiz, D-Calif., called on immigration authorities to conduct more “meaningful medical screenings” after the deaths of 8-year-old Felipe Alonzo-Gomez on Christmas Eve and 7-year-old Jakelin Caal Maquin earlier this month. The Trump administration has yet to name the boy who died, but Congressional Democrats identified him as Felipe Alonzo-Gomez.

Those medical screenings would include a questionnaire, a review of any symptoms, medical history, a check of a migrant’s vital signs and consultation with medical personnel, Ruiz said.

“We need to think like physicians and think like humanitarian aid specialists and we need to match the response to the needs that we are seeing,” he said.

Castro said Ruiz was also working on drafting legislation that would set “basic or minimum health care standards” for Customs and Border Protection and Immigration and Customs Enforcement as migrants make their way through immigration custody.

CBP said Tuesday that the 8-year-old died minutes before midnight on Christmas Eve in New Mexico from unknown causes. His death followed that of Jakelin, who died on Dec. 8. Her body arrived in her home country of Guatemala on Monday.

Rep. Joaquin Castro, D-Texas. Alex Edelman / Getty Images file

Rep. Nancy Pelosi, D-Calif., the incoming speaker, also called for a congressional investigation into the deaths.

"Democrats call on Homeland Security’s Inspector General to immediately open an investigation into Felipe Alzono-Gomez’s death,” she said in a statement. “The Congress will also investigate this tragedy and the heartbreaking death of Jakelin Amei Rosmery Caal Maquin, to seek justice and ensure that no other child is left to such a fate.”

Meanwhile, Homeland Security Secretary Kirstjen Nielsen said in a statement Wednesday that she has asked the Coast Guard Medical Corps to assess CBP’s medical programs and make recommendations for improvements. Both CBP and ICE are under the Department of Homeland Security.

"This tragedy, the death of a child in government custody is deeply concerning and heartbreaking," she said.

Nielsen said she has also asked for assistance from the Department of Defense “to provide additional medical professionals” and that moving forward “all children will receive a more thorough hands on assessment at the earliest possible time post apprehension — whether or not the accompanying adult has asked for one.”

"I will be traveling to the border later this week to see first-hand the medical screenings and conditions at Border Patrol stations," she said.

She added that there were six deaths in CBP custody in fiscal year 2018, none of which were children, and prior to the two deaths this month it had been more than a decade since a child died in their custody.

A boy carries a picture Jakelin Caal while her coffin is carried to the cemetery in San Antonio Secortez, Guatemala, on Dec. 25. Johan Ordonez / AFP - Getty Images

Late Monday, CBP said Border Patrol will conduct “secondary medical checks” on all children in its custody. The agency told NBC News in a previous statement that initial medical screenings consist of agents documenting any observed or reported medical needs which require emergency treatment by a medical professional.

Castro and Ruiz said they had not been provided details as to what those secondary or more thorough assessments would look like.

CBP did not immediately respond to questions on what those additional medical checks would look like or if any medical personnel or EMT–trained agents were present at any of the facilities Felipe and his father were held at.

Felipe and his father were apprehended on Dec. 18 in El Paso, Texas, and held in a processing center there before being transferred to the El Paso Border Patrol Station and then transferred again to the Alamogordo station in New Mexico on Dec. 22, CBP said.

On Monday morning, a processing agent noticed “the child was coughing and appeared to have glossy eyes” and transferred the boy to the Gerald Champion Regional Medical Center, CBP said. The child was initially diagnosed with a common cold and given Tylenol, but when the boy was evaluated for release, hospital staff found a fever and he was held for an additional 90 minutes before being released on Monday afternoon, CBP said. The boy was given prescriptions for amoxicillin, an antibiotic, and the painkiller ibuprofen.

CBP said the boy and his father were transported to a temporary holding at the Highway 70 checkpoint.

At 7 p.m., the child appeared nauseous and vomited and his father declined further medical assistance as the child was feeling better, CBP said.

At 10 p.m. the child “appeared lethargic and nauseous again” and CBP said no EMT was on duty at the highway checkpoint so they made the decision to return the two to the medical center, but the boy “began to vomit and he lost consciousness” on the way to the hospital. He was pronounced dead at 11:48 p.m. on Christmas Eve, CBP said.