GEOFF BENNETT: Since the start of President Trump's second term, the administration has detained nearly half-a-million immigrants in the U.S.

That's according to a new report.

But the number of children they leave behind and what happens to them, most of whom are U.S.

citizens, is largely unknown.

Our White House correspondent, Liz Landers, has more -- Liz?

LIZ LANDERS: Geoff, that new research from the Brookings Institution finds that, by detaining 400,000 immigrants over the past 14 months, the Trump administration also stripped about 145,000 American children of at least one parent.

Data from the Department of Homeland Security calculates a much smaller number, 60,000.

Tara Watson is one of the Brookings' studies authors, and she joins us now to discuss that discrepancy and more.

Tara, thank you so much for joining us.

TARA WATSON, Senior Fellow, Brookings Institution: Glad to be here.

LIZ LANDERS: The Washington Post recently reported a story about a woman who was in the United States illegally and was deported without her toddler, Orlin Hernandez Reyes, who was a U.S.

citizen.

The child was left with a violent uncle, who allegedly murdered him.

How much information is the government collecting on cases where a U.S.

citizen child is left without their parent?

TARA WATSON: There's surprisingly little information provided by the government about the children of people who are detained or deported.

The government does produce annual statistics, but we believe those to be quite an undercount.

Probably only about half of children are recorded in that way, both because ICE doesn't always follow the directive to ask people whether they have children in the U.S., but also because immigrants don't always feel comfortable sharing that information, for fear of further enforcement against their family.

LIZ LANDERS: You mentioned ICE asking those questions.

They're supposed to ask detainees about their parental status.

Why doesn't that always happen?

TARA WATSON: I think ICE isn't really in the business of child welfare.

That's not their primary mission.

And when we're talking about citizen children who they wouldn't be doing an immigration enforcement related to, they would prefer to just move on.

And if the person that they're arresting or detaining doesn't bring up a child, they may have an incentive to not ask the question.

LIZ LANDERS: How common is it for the children to remain here when their parent does get deported?

TARA WATSON: We don't have perfect information about that.

Again, this is an area where there isn't enough transparency.

We believe that, in most cases, the children, especially the citizen children, are staying in the U.S.

with friends and family.

Unfortunately, sometimes, as in the case you mentioned earlier, there isn't a great option for a parent to leave the child with, and they end up choosing a situation that may not be great for the child in the long run.

LIZ LANDERS: Who are these citizen children that get separated from their parents?

I know you guys gathered some information about what parts of the country they're from, how old they are, the parents' country of origin that they're deported back to.

Paint that picture for us.

TARA WATSON: Sure.

So the children are all ages.

About a third of them are under age 6.

And, of course, it goes up all the way up to age 17, which is the oldest age we consider to be a child.

They're largely U.S.

citizens, as was said earlier.

And their parents come from a range of countries, but the most dominant countries are in Latin America and Central America.

LIZ LANDERS: What happens to these children when their parents are detained?

What are the welfare systems in place and what's the emotional support for these kids that supposed to be offered?

TARA WATSON: So, really, there is no system in place, which is part of what motivated us to do this study and try to better understand, at a minimum, how many children we were talking about.

The -- ICE doesn't have an obligation to provide for the welfare of those children, as long as someone is taking care of them.

The child welfare system also doesn't have an obligation to get involved unless there's an accusation of abuse or neglect.

So, really, there is no system that is looking out for these kids, making sure the placements they're in are safe.

And I think that's a problem.

LIZ LANDERS: You mentioned that there are potential gaps in the government data right now.

How confident are you in your data?

Explain this methodology.

TARA WATSON: I can explain how we came up with these estimates.

Since we didn't have numbers from the government, what we had to do is take information on the detainees, which we do have access to.

We know things like what country they're from, how old they are, whether they're male or female, whether they're married.

And then we turn to survey data.

We look at survey data of undocumented immigrants who are living in the U.S.

And we say, well, we know a certain fraction of people who have a certain age or marital status have kids, and they have a certain number of kids per parent, and so we applied those numbers to the detainee population which we do know about.

LIZ LANDERS: Why is this research necessary?

What's important for the public to understand about your findings?

TARA WATSON: I think the most important thing is that the children that we are deciding collectively to separate from a parent or both parents need to have their well-being ensured, and we don't have a system in place for that.

As a first step, the government should be providing data on how many children and what's happening to those children.

For example, some children are being put on deportation planes even as U.S.

citizens.

They're not being formally deported because they're citizens, but they may be going with their parent's request to the country of origin of the parent.

We don't have any statistics that are publicly released about this.

So the government should be sharing what they know, and they should be ensuring that the data on the children is collected, so we can make sure that the kids are in good situations.

LIZ LANDERS: Tara Watson, thanks so much for joining us.

TARA WATSON: Thanks.