(CNN) On your 18th birthday, immigration officials will come for you, a lawyer explained. You will be shackled, you will be placed in an orange jumpsuit, and you will be taken to jail. "But I need you to know you are not a criminal."

This is how Allison Norris, toll litigation staff attorney at Americans for Immigrant Justice, prepares her teenage clients in federal migrant detention shelters who are nearing age 18 without the prospects of a suitable sponsor to whom they can be released.

One of these clients is Veronica, whose name has been changed to protect her identity for fear of retribution. At age 17, she arrived in the United States alone, fleeing sexual predators in El Salvador.

Between the time Veronica arrived and when she turned 18, just over four months, Norris says, she attempted to find a sponsor. But none of the family friends who applied met the extensive list of requirements of the Office of Refugee Resettlement in order for her to be released from the shelter for migrant children in South Florida where she was detained.

On her 18th birthday, she woke up scared, wondering what would happen to her, Veronica said. Norris' detailed warnings had not exactly calmed her down.

At 8 a.m. on her birthday, immigration officials arrived at the shelter. She was placed in ankle shackles and put in a "very cold room" for hours before being taken into adult detention, Veronica said.

In the months that followed, Veronica describes feeling depressed, crying every day and losing hope. Because she wasn't serving a specific sentence, she had no idea how long she'd spend in detention.

With hours to fill in a cell she shared with three older women, she relived in her mind the attacks she suffered in El Salvador.

"I didn't know what was worse: to have died in El Salvador or to be locked up," she said.

Veronica is part of a group of kids known as ORR age-outs. When unaccompanied minors arrive in the United States, they are placed in the custody of the Office of Refugee Resettlement, part of the US Department of Health and Human Services, a humanitarian agency in nature.

Once they turn 18, teens are moved into the custody of the Department of Homeland Security -- more specifically, US Immigration and Customs Enforcement, a law enforcement agency known as ICE. Migrant youth cannot, by law, stay in the shelters that housed them before they turned 18.

"I have interviewed the children right before they turn 18 and they go into these facilities," said Yenis Castillo, a forensic psychologist with the nonprofit advocacy group Physicians for Human Rights. "All the kids I interview are terrified."

In the weeks leading up to their 18th birthdays, Castillo said, she has seen teens act out, develop chronic headaches or high blood pressure, become depressed and even become suicidal.

"When people undergo trauma, they live in a constant state of alert, and on top of that, then we are sending them to prison," she said.

Neha Desai, director for immigration at the National Center for Youth Law, has toured immigrant child detention centers across the country. "Everywhere I go, the kids that are in most extreme and visible distress are the ones that are approaching age-out. There's so much anxiety in that period of time," she said.

The Trafficking Victims Protection Reauthorization Act, passed in 2000 and reauthorized in 2008 and 2013, states that when unaccompanied immigrant children in the custody of the Office of Refugee Resettlement turn 18, ICE "shall consider placement in the least restrictive setting available after taking into account the [individual's] danger to self, danger to the community, and risk of flight."

"What we've seen is that they very rarely do," said Xiaorong Jajah Wu, immigration attorney and deputy program director at the Young Center for Immigrant Children's Rights. Wu oversees offices in Houston and Chicago, where she says it is the child's attorney or child advocates who put forth alternatives to adult detention, "basically begging ICE not to take these kids on their 18th birthday."

Wu said her team has not seen what they'd consider "any level of thought" being put into the decision of whether to take a migrant youth into adult detention.

In California, Lindsay Toczylowski, an immigration attorney and founder and executive director of the immigrant Defenders Law Center, says the move into adult detention has become the norm rather than the exception for teens over the past two years.

"What we've seen is a lack of discussion for ICE when deciding whether or not they are going to take a kid into custody," she said. Toczylowski also worries about the way in which this is done, which she describes as "overkill," considering that these are typically petite teens from rural communities in Central America who have committed no crimes.

Kate Melloy Goettel, senior litigation attorney at the National Immigrant Justice Center, noted that "Congress really understood that these kids are vulnerable. And now we are just trying to get ICE to understand that they have obligations under the law to really try to find options other than detention."

These options, Goettel explains, includes placement with family members, non-family sponsors, shelters, group homes and institutional placement.

Jennifer Elzea, press secretary for ICE, wrote in an email that "custody determination is made by ICE on a case-by-case basis, taking into account the totality of the individual's circumstance, to include flight risk, threat to the public and threat to themselves." Elzea acknowledged understanding the requirement that the agency consider the least restrictive setting available and to consider alternatives to detention.

Goettel is part of the team of attorneys at the National Immigrant Justice Center who, in March 2018, sued Homeland Security and ICE on behalf of two migrant teens who were placed in adult prisons when they turned 18. The lawsuit alleges that ICE "failed to consider them for placement in 'the least restrictive setting available' and to provide them with meaningful alternatives to detention, as required by amendments to the Trafficking Victims Protection Reauthorization Act."

According to documents obtained from the Office of Refugee Resettlement as part of the class-action lawsuit, 528 children aged out of custody in 2015. The number doubled to 1,044 in 2016, remained about the same at 1,091 in 2017 and, in the first half of 2018 alone, included 1,240 kids.

In November, Health and Human Services confirmed that there were a record 14,000 unaccompanied children in Office of Refugee Resettlement custody.

Since the lawsuit was filed, a judge required ICE to reassess the custody of the two original teens and place them in the "least restrictive setting possible." In August, the court granted a motion for class action certification, meaning the lawsuit against Homeland Security is now on behalf of all unaccompanied migrant children in custody of the Office of Refugee Resettlement who "age out" when they turn 18.

When asked about the lawsuit, Elzea said, "ICE does not comment on pending litigation"

As for Veronica, she spent just over two months in adult detention. Norris, her attorney, says that a family friend with lawful status was able to get all required documents quickly, and Homeland Security released Veronica to live with her.

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But, Norris says, the process can take much longer for other teens, many of whom lose hope while in detention and ask to be sent back to their home countries.

"They fought all this way to come here, raised all this money to go on this very dangerous journey to escape horrific violence, and all of a sudden they've been in detention for three months, and they're like 'just send me back. I can't take it anymore,' " she said.