The Trump administration on Thursday faces its court-imposed deadline to reunite 2,551 children it forcibly separated amid concerns from advocates and attorneys that parents were coerced into being deported without their children.

The US homeland security department (DHS) secretary, Kirstjen Nielsen, said the government was “on track” to meet the deadline, during a meeting on Wednesday with roughly 20 members of the Congressional Hispanic caucus.

Many of those present told the Associated Press that Nielsen’s comment was met with open disbelief and anger. Representative Joaquin Castro, a Democrat from Texas, tweeted that Nielsen told the caucus: “I am not a racist. Nobody believes families should be separated.”

The Trump administration announced Thursday that more than 1,800 children had been reunited with parents and sponsors. On Tuesday, the government said that 463 parents had been deported without their children, alarming attorneys who doubt immigration authorities clearly explained to parents what they were agreeing to do.

Michelle Brané, director of migrant rights and justice at the Women’s Refugee Commission, said: “We have no idea what choices those 463 parents made, and what information they were given and whether they had any choice. It’s clear from early on in this process parents were being deported with no reference and no attempt or no choice to be reunified with their children.”

DHS said in court documents it complied with orders to provide immigrants with notices of their rights in Spanish and English.

One document, prepared by the American Civil Liberties Union (ACLU), includes three checkboxes depicting the stark reality parents immediately face if they lose their immigration case: “I would like to take my child with me”, “I do NOT want to take my child with me” and “I do not have a lawyer and I want to talk with a lawyer”.

Lee Gelernt, the ACLU attorney leading the lawsuit against the Trump administration, said tracking the deported parents down would be “an enormous task”.

“At the moment they [the government] have not laid out anything close to a plan for how they are going to do it,” Gelernt said.

To help locate parents who were deported to Central America, including those who do not know where in the US their children are, the child advocacy group Kids in Need of Defense (Kind) on Thursday announced a special transnational reunification program that would also provide affected families with legal and psychosocial services.

Attorneys are also worried about what happens to reunited families, who are either held in family detention or released as they wait for their immigration case to be tried.

Lisa Frydman, Kind’s vice-president of regional policies and initiatives, said: “Kids are really confused, had major trust violations, and some of them are angry at their parents because they think it was their fault. There is a lot of confusion and a lot of harm that these children experienced. Some children have stopped communicating – selective mutism.”

Kind is handling the cases of more than 100 children and, like other child advocacy groups, said it was not getting consistent advanced notice about what was happening to the children it represents, who are often transported in the middle of the night.

Maria Odom, Kind’s vice-president of legal services, said two children the group was particularly concerned about were a nine-year-old and 14-year-old who were discharged from a shelter but their mother was deported before they could be reunited with her. “We have not been able to locate the children and we are mentioning them as an example of how there are children who have been placed in this black hole of reunification,” Odom said.

Advocates are encountering the same problems with adults, who they said were also being reunited and released at night with little or no warning to their lawyers. Volunteers wait in bus shelters, detention center parking lots and at churches with food, bus tickets and legal assistance for the families.