They’ve been arriving in New York City in the dead of night. Quietly placed in temporary foster care, hundreds so far, they’re among the thousands of children that the US government has separated from their parents.

No one can say when — or if — they’ll ever see their parents again.

President Trump’s executive order purports to end the policy of family separation that Attorney General Jeff Sessions had unveiled six weeks earlier and which Homeland Security Secretary Kirstjen Nielsen had said didn’t exist, and replace it with family incarceration. The order, however, is conspicuously silent on reunification.

Absent a major effort initiated and led by Congress, reuniting these families will be difficult, if not impossible. There is no system in place for this purpose, nor at this time is there a coordinated effort to reunite families. It’s evident that the Trump administration tore families apart without giving any thought to how they could be put back together.

The government may not even be tracking the children or collecting relevant information. A 2017 report on family separation found, “There is no agency-wide policy defining what constitutes a family, no traceable documentation of those familial relationships, nor a requirement for documentation of all family separation incidents.”

The government has announced that parents should call the Office of Refugee Resettlement to locate their children. Yet my organization has been visiting detention centers, and many of the parents in these facilities weren’t even aware of this avenue, let alone the toll-free phone number. Some women who’ve tried the number say there was no answer. In only one facility did we meet a staff member who seemed to want to help parents find their children.

The task of putting families back together has fallen primarily to attorneys and advocates, whose searches thus far are largely ending in frustration. According to The Washington Post, the Texas Civil Rights Project has been able to track down only two children of the 300 parents it represents.

My organization represented a teenage mother in immigration detention who had been separated from her 2-year-old shortly before child-snatching became official national policy. After the mother was released, it took three weeks, and a great deal of pressure, to reunite her with her son — and this was a rare case where we actually knew where the child was being held.

The situation is dire but far from hopeless. Make no mistake, we can put these families back together. Here’s how we can begin to do so:

First, we should resist the effort of the Trump administration to expand so-called family detention. Locking up children with or without their parents is cruel. Voluminous evidence shows that even short-term detention can damage the long-term physical and emotional health of children.

The US government should keep immigrant families both together and out of detention. Parents who have legal counsel or participate in family case-management programs, like the highly successful one the Trump administration canceled last year, overwhelmingly appear for their immigration hearings.

Second, Congress must act. Congress should require Immigration and Customs Enforcement and Customs and Border Protection to do an immediate audit of all adult detainees, asking if they had children taken and for all identifying information. Congress should require ORR to do the same: Create a database of all children taken from their parents. It should get whatever information it can about parents from children who are able and willing to talk and assume that nonverbal children were separated until proven otherwise.

Congress should then empower an independent committee to connect the dots between these two data sets and to work intensely on unresolved cases.

At the same time — immediately — Congress should require ICE’s Enforcement and Removal Operations to freeze the deportation of parents who don’t know where their children are. No parent who is trying to be reunited with her child should be deported without that child, a practice that can lead to permanent separations. ICE should also release the separated parents from detention to facilitate reunions as quickly as possible.

The policy of family separation has drawn opposition and outrage from politicians of both parties. Even if the White House won’t act, Congress has the power to put these families back together. All they need, now, is the will.

Eleanor Acer is the senior director of Refugee Protection at Human Rights First.