It took 85 days for Olivia Caceres to get her baby boy, pulled from his father's arms at the US border, a traumatic experience many more parents face to reunite with children separated under President Donald Trump's immigration policies.

Now nearly 20 months old, Mateo was returned to his family on 8 February after a battle across borders, officialdom and languages.

He was filthy and terrified of the dark, his mother said. Months later, the boy still screeches even as Ms Caceres rocks him on her chest, sometimes until dawn.

The Salvadoran family's story of struggle in US immigration detention presaged what was to come: President Trump's "zero tolerance" policy that led to more than 2,300 migrant children being separated from parents in recent weeks.

Ms Caceres' quest to find her child foreshadows the long road ahead for many immigrant families after Mr Trump reversed the separation policy and directed agencies to begin reuniting families this week.

Last year, Ms Caceres, her husband Jose Demar Fuentes, and their children Mateo and five-year-old Andree, fled El Salvador where gangs had demanded protection money, and crossed Mexico in one of the regular 'caravans' of migrants that travel together for safety.

On 12 November, Mr Fuentes sought asylum at the US-Mexican border, with Mateo in his arms, citing the gang threats. Ms Caceres was due to follow a few days later with Andree.

But she heard that US immigration officials had taken Mateo from his father on 16 November, as Mr Fuentes was being transferred to a San Diego detention centre. Still in Tijuana, she began a frantic search for her son.

When she finally got Mateo back in February, "he looked like he hadn't been bathed in three months", said Ms Caceres in an interview with Reuters this week from Los Angeles.

"It was very hard to see the condition he was in. I don't want to imagine that mountain of children, how they care for them," she said, choking on tears.

The potential consequences of such separations include impacts on brain development and mental health, as well as persistent behavioural and academic problems, especially for under-fives, child development experts say.

That first night, Mateo was inconsolable as Ms Caceres held him tight, whispering he was "with your mama," she said.

Ms Caceres had finally located Mateo at a facility in Texas. The phone number for the facility she provided to Reuters is registered to International Educational Services Inc (IES).

A nonprofit, IES closed its centres in Texas in March after losing funding from the Office of Refugee Resettlement, according to local media reports. A spokeswoman for the Texas Health and Human Services Commission confirmed that the facilities were inactive.

That agency found various violations during its inspection of IES facilities, including improper administration of medication, according to the agency's website.

In a statement to local media, IES did not say why it shut the facilities. ORR did not immediately respond to request for comment. There was no answer at IES' listed phone number or from employees' emails. Texas HHS did not provide a reason for the closure.

'He's here'

Locating Mateo took Ms Caceres a week of phone calls to similar institutions on numbers she was given after speaking to a hotline for immigrant parents separated from their children.

Ms Caceres called some numbers ten times to get an answer. One official said Mateo was not entered into the system at all.

For a time, it seemed her son did not exist in US bureaucracy.

On the seventh day of calls, late in November, she got through to IES.

"Yes, he's here," the person at the end of the line said."Are you the mother?"

Shaking with relief, she asked for information on Mateo's health, his mood, how he was being fed and how he was sleeping.

They would give her the information, they said, but first needed proof of parentage.

With help from a pro-bono lawyer, Ms Caceres emailed the documents she had: Mateo's birth certificate, a hospital form with the baby's footprints and her Salvadoran identity card.

The director of the Texas facility demanded a DNA test. In the end parentage was established with the help of a representative from the Salvadoran consulate in Texas who certified the documents, Caceres said.

It then took time to convince IES to let her talk to Mateo and then only by sending a five-minute video of herself to the facility. Over the phone, she listened to Mateo cry as he was shown the video, unable to locate the source of her voice.

"He thought she was there to pick him up," her attorney Erika Pinheiro said. "He became very distraught after the call."

Officials at the centre told Ms Caceres they had no knowledge of her case nor how her son came to them. Immigration authorities just sent them the babies, they said, according to Ms Caceres.

Ms Caceres could not fly to fetch her son herself because of limitations on her movements, tracked by an ankle bracelet after she crossed the US border with Andree and sought asylum. She was staying with relatives in Los Angeles.

At one point she was asked, she and her attorney said, to pay $2,000 so an official could deliver Mateo from Texas. Ms Pinheiro said the ORR specialist on the case ultimately agreed to waive the fee.

Searching for a better future

Back home, Mr Fuentes, 30, and Ms Caceres, 29, ran a shop selling artisan shoes. Like many small business owners, they were forced to pay a weekly "war tax" to Mara Salvatrucha, MS-13, one of two brutal gangs with domains across the country.

When the tax doubled from one week to the next, to $100, they could no longer afford to pay, Ms Caceres said. But missing payment, she said, meant death. The family fled.

For reasons that are unclear, US immigration officials pulled Mateo from Mr Fuentes' clutch as he was being transferred to San Diego's Otay Mesa detention centre, along with the children of three other fathers. He was not told where the baby was sent.

A Customs and Border Protection official told Reuters this week the agency determined he and his minor son were citizens of El Salvador with no legal status to enter the United States, and handed them to US Immigration and Customs Enforcement (ICE).

At the time, an ICE spokeswoman released a statement saying Mr Fuentes did not have documents to verify he was the father and the child was too young to answer officers' questions.

Ms Pinheiro and other advocates say Mr Fuentes' Salvadoran identity documents and Mateo's birth certificate were evidence of their family connection.

Mr Fuentes sought asylum alone with Mateo because the boy was sick after their journey from Central America, much of it undertaken on the open top of a freight train, and they wanted to get to the United States to seek treatment, Ms Caceres said.

Mr Fuentes, trained as a journalist, still remains detained in Otay Mesa, denied parole and family visits, according to Ms Caceres and Ms Pinheiro.

"It's difficult for me to take in that I am a risk of flight when I handed myself in and asked for asylum," he wrote in an letter to Otay Mesa authorities seen by Reuters.

"I came to find security for my family and what I obtained was separation from my son, who was one year and two months old."

Mateo can now say "pa" and "ma," and when he explodes into violent crying, the only way Ms Caceres finds to soothe him is with those words as she rocks him.