Lee Gelernt is happy that some young children will be reunited with their families by a court-ordered deadline on Tuesday. But, the lawyer says he's disappointed that not all children will see their parents.

On Monday, Justice Department lawyer Sarah Fabian said that at least 50 children under five years of age will be released and reunified with their parents, but added that the Trump administration won't meet the deadline for all of the 102 children, as they are still working to confirm the relationships between the adults and children in custody.

The Tuesday deadline is in response to a lawsuit filed by the American Civil Liberties Union which won an injunction last month to speed up the reunification of migrant families that were separated under the Trump administration's "zero-tolerance" policy at the border.

Gelernt, an attorney with the ACLU, spoke with As It Happens guest host Rosemary Barton about the administration's announcement.

Mr. Gelernt, what did the court decide today about these children under five, who should be reunited with their families?

We are thrilled that more than 50 little children will be reunited with their parents by tomorrow, but we are extremely disappointed that it's not a greater number.

The judge made clear that he wants to see us tomorrow and get updates and continue the process. He intends to be very hands on so the government can no longer make vague promises about reunification and will hold the government to very specific, tight deadlines.

Only about half the children under age five who were separated from their parents at the U.S. border will be reunited with their families by Tuesday's court-ordered deadline. (John Moore/Getty Images)

And why did the government say they can't meet the deadline?

The government has offered a variety of reasons why they can't reunite different families. A few of the justifications are legitimate. If the parent is actually in criminal custody now, reunification cannot occur.

For the other parents, I think there just hasn't been enough of an effort made to locate the parent. And that's extremely troubling.

The other problem is the government is using a very lengthy, cumbersome reunification process that was designed for children who were genuinely unaccompanied and are being given to someone coming forward to claim them, rather than this situation where the child was forcibly taken from the parent. We are just asking that the parent be given back their child.

How much of this is about the fact that they didn't really track or think about how they were going to track these kids to begin with?

I think what the hearing on Friday and today revealed is what a lot of people suspected, that there really wasn't a proper tracking system for these families and the government is now pulling information from a variety of sources and that's one of the reasons why the reunifications are taking so long.

And today the government revealed that for one child, they don't even have a parent's name, much less make contact.

Lee Gelernt, an attorney for the American Civil Liberties Union, speaks after a hearing in San Diego. (Gregory Bull/Associated Press)

So what happens in that kind of situation?

We hope the government will find that parent, and we will also be looking.

One of the reasons that we asked the court to order the government to provide us a very specific list of the families and any information the government had about those families, is so that we can mobilize the enormous volunteer effort on the ground to help find parents and children.

And how old is that child?

That child is a three-year-old boy.

How are these children?

The children are extremely traumatized, as the medical community expected they would be.

I've talked with one family, a four and 10-year-old boy who were separated for months. Now they're reunited, but the four-year-old boy continues to ask his mother at night, "Are they going to come and take me away again?"

How long do you think it will take then for the reunification for these very small children to happen, with their family?

We are going to propose within 48 hours of contacting a parent who is in the U.S., and within one week of contacting a parent who's already been removed to another country.

Wilson Romero boards a bus in El Paso, Texas. Romero was separated from his daughter, was leaving Texas for California to stay with family members until he can be reunited with his daughter who is in a facility in Arizona. (Matt York/Associated Press)

And if they continue to drag on, what would you ask the judge to do in that instance?

I don't anticipate them dragging on. I think now that the court is requiring them to literally submit information almost twice daily, I think we're a long way from the point where the government is going to have to be sanctioned by the court.

For the more than 50 children who the government says will be reunited tomorrow, what are you expecting that moment to be like for those kids and those parents?

I have seen prior reunifications and it is heartbreaking to see the parents and child come together.

What people need to remember is, it's not just the amount of time they've been separated, but for many of these families there was the feeling that they may never see each other again. So it is just overwhelmingly emotional.

Written by Sarah Jackson with files from Associated Press. Interview produced by Kevin Robertson. Q&A has been edited for length and clarity.