At least seven children are known to have died in immigration custody since last year, after almost a decade in which no child reportedly died while in the custody of U.S. Customs and Border Protection.

The string of cases continue to raise questions around the conditions in which migrant children are being kept at a time when a growing number of migrants, many of them Central American parents with children, are presenting themselves at the border to seek asylum.

Aside from the fact that children may have underlying health conditions, most are reaching the United States after arduous journeys during which they have had little access to clean shelter and proper provisions. Many are leaving impoverished and drought-stricken regions.

But the deaths under President Donald Trump's watch have health professionals and some advocates questioning whether the administration's immigration policies — particularly keeping minors in custody for longer periods — are contributing to more minors getting sick and dying while in custody or shortly after they are released.

“Children are not like adults. They get sick more quickly and each hour of delay can be associated with serious complications, especially in cases of infectious diseases. Delays can lead to death,” Dr. Julie Linton, co-chair of the immigrant health special interest group at the American Academy of Pediatrics, told NBC News.

The most recent known case is that of Carlos Gregorio Hernández Vásquez. The teenager died in CBP custody this month after being diagnosed with the flu, an infectious disease.

In December, medical examiners concluded that 7-year-old Jakelin Caal Maquin, who also died in CBP custody, succumbed to "a rapidly progressive infection" that shut down her vital organs. CBP sent Jakelin on a 90-mile bus ride to another location after she was taken into custody, even though her father had told officials she was vomiting and feeling ill before they left.

CBP officials said last year that Jakelin waited an hour and a half to receive emergency medical care after showing symptoms.

Deaths of several other migrant children were reported in just eight months following her death.

“We do not need to be talking about the prolonged detention of children. It is dangerous,” Linton said.

Seven months before Jakelin's death, 1-year-old Mariee Juarez died after being released from U.S. Immigration and Customs Enforcement custody.

Yazmin Juarez and her daughter, Mariee, came seeking asylum from Guatemala. Courtesy Yazmin Juarez

Mariee died from complications of a respiratory illness her mother and lawyers say she allegedly developed while detained.

CBP holding facilities are “basically concrete floors with mats and barbed wire fencing and bright lights 24/7,” Linton said. “That can be a very disorienting environment to children.”

Leah Chavla, an international human rights lawyer and policy adviser at the Women's Refugee Commission, has worked with families who have raised many concerns over CBP facilities being “inadequate.”

“Families have come with concerns about lack of hygiene, being crammed into holding cells, being served food that has not fully cooked or nutritionally appropriate for kids … being woken up throughout the night," Chavla told NBC News.

The CBP holding facilities are often referred to by the people held in them as "hieleras," which translates to icebox or cooler, because of their frigid temperatures. A Human Rights Watch report about these conditions pointed out that children were sleeping under thin Mylar blankets or foil wrappers.

Wilmer Josué Ramírez Vásquez, a 2½-year-old, died this month after being detained by Border Patrol in early April and spending about a month in a hospital, where he was diagnosed with pneumonia.

Carlos, 16, had been held in such a facility before being diagnosed with influenza A. He died May 20. The teenager had spent one week in CBP custody, even though legally he should have not been there for more than three days.

U.S. laws require CBP to transfer minors into the custody of the Office of Refugee Resettlement (ORR) at the Department of Health and Human Services (HHS) within 72 hours unless there are "exceptional circumstances.

A CBP official told NBC News via email that "the standard is 72 hours or less, but with the on-going crisis that has been difficult to maintain at times."

The official stated that despite the fact that the number of migrant families and unaccompanied minors remain at peak levels, U.S. Border Patrol continues to conduct processing of unaccompanied minors in a little over a day, on average, across the southwest border.

The official added that the high number of children requiring placement with HHS-ORR exceeds their available shelter spaces so the minors spend more time in Border Patrol facilities until then.

Under ORR, children are supposed to have access to a network of state-licensed or government-funded private care providers, as well as education, health care and case management services, Linton explained.

And yet, Carlos was placed back in CBP custody after he was diagnosed with flu-like symptoms, an official from the agency previously told NBC News.

“Kids are not being processed quickly enough under CBP,” Chavla said. “Filing complaints to elevate some of these concerns has been one of a couple of mechanisms used to push CBP into following the rules, but there are still some real doubts about how serious they’re about this.”

Felipe Gómez Alonzo, 8, also was held in CBP custody for nearly one week before he died on Christmas Eve. Medical investigators later determined the boy had been suffering from the flu while he was under the agency’s care.

“A child should never be returned to a processing center to recover from an illness,” Linton said. “As a pediatrician, I would never suggest for a kid to heal in a stressful environment with concrete floors.”

Even though ORR is more equipped than CBP to house minors for a longer period of time, children have also died while in ORR care or shortly after being released from immigration custody.

Darlyn Valle, 10, died in September after entering ORR custody, but her death was revealed to the public nearly eight months after it had happened.

The girl entered ORR custody on March 2018 “as a medically fragile child with a history of congenital heart defects” and remained in its custody until September, the agency told NBC News in a statement. During that time, Darlyn underwent a surgical procedure at a facility in Arizona and complications later left her in a coma.

She was then taken to Nebraska, just three days before her death, in an effort to reunite her with her mother. She died due to fever and respiratory distress, ORR said.

ORR said it provides routine and emergency medical and mental health care to all children in its care, including an initial medical exam, follow-up care as appropriate and weekly individual and group counseling sessions with care provider clinicians.

“The government kept a sick child in its custody from March to September. That’s 7 months she could’ve been in the arms of her mother,” Al Otro Lado, a nonprofit legal services organization, wrote on Twitter.

Juan de León Gutiérrez, 16, died of health complications under ORR care on April 30 after officials at a detention facility in Texas noticed he was sick.

Juan de Leon Gutierrez in a March 2017 photo. Jimmy Cristian Gutierrez Garcia / via AP

CBP apprehended nearly 99,000 migrants who entered the U.S. without authorization last month.

Nearly 60 percent of them were family units, according to CBP numbers. Both figures have continued to rise each month since January. Although apprehensions are still well under the historic highs of the late 1990s and early 2000s, the majority of migrants then were adult men from Mexico — not asylum-seeking families with children.

The administration has been limiting the number of people walking up to a legal port of entry on the U.S. side of the border and asking for asylum. Advocates say that has led to more people crossing the border illegally, which is contributing to Border Patrol agents ending up with overcrowded processing facilities and holding facilities.

“CBP’s priority is law enforcement. They don’t necessarily have the conditions to keep children for a long period of time,” Linton said.

Congressional calls for oversight and investigations are always welcomed to see what to avoid and what can be done better, Chavla said, especially to look into how CBP is implementing its own guidelines that outline the conditions and resources the agency has to provide to children in their custody.

“Guidelines are not binding, so it’s important to have a critical look at what’s going on and how the guidelines can be made binding,” Chavla said.

Acting director of the Department of Homeland Security Kevin McAleenan said during a recent budget hearing that more than 100 certified medical practitioners have been deployed to the two busiest sectors. But when asked if every child in CBP custody had access to a pediatrician, McAleenan answered with a confident “no.”

“There’s a need for urgent and thoughtful engagement of pediatricians in every step where children are involved,” Linton said.

Even before the latest deaths, the American Academy of Pediatrics recommended that immigration agencies should better train staff on how to respond to health-related emergencies and prioritize “the thoughtful release of children, more case management efforts and humane safe conditions,” Linton said.

And yet, she said, she and other health professionals continue to ask why there seems to be a lack of urgency to improve the conditions in which migrant children are being held.

“We would love to know the answer to that question,” she said.

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