Far more American children have likely been separated from their parents during immigration sweeps than previously understood, according to a report by the Washington, D.C.-based think tank Brookings.

The report published Monday estimates more than 100,000 U.S. citizen children have had a parent detained since President Donald Trump’s mass deportation campaign began last year. The analysis cites reporting from ProPublica on the detention of parents, which can often lead to family separations.

During Trump’s first administration, a policy of family separation at the U.S.-Mexico border ended after widespread outrage. Now, the breakup of families is happening amid sweeps by immigration agents across the country.

About 400,000 people have been detained by immigration agents since Trump returned to office, Brookings noted. But it’s nearly impossible to know how many family separations that has caused, since the administration does not track it.

Families are also now being split up in ways that are more dispersed, more hidden and harder to track.

Brookings created its estimate by using census information to approximate the number of children that detainees have. It estimated that roughly 200,000 children, including 145,000 American kids, have had a parent detained. The think tank notes that the actual number could be somewhat higher or lower.

ProPublica used a different, more conservative, approach that relied on government data obtained through a public information lawsuit by the University of Washington. We found that in just the first seven months of Trump’s second term, at least 11,000 American children had a parent detained. We also found that Trump has been deporting about four times as many mothers of American children per day as President Joe Biden did.

As we noted, our figures are almost certainly undercounts. For instance, the government data relies on detainees self-reporting whether they have children. In some cases, agents may not ask and parents may not share details about their families out of fear of what might happen to their children.

“There are a lot of families that are in the situation that are not being written down,” said Tara Watson, one of the authors of the Brookings report. It’s “important both for transparency and from a child health and wellbeing perspective to know what’s happening to the kids. How many of them are leaving the U.S.? How many of them are staying in the U.S. with close family? How many of them do we really not know what their situation is?”

ProPublica also followed multiple families through their sudden separations and found a wide variety of outcomes for the children.

Doris Flores, a mother from Honduras, was separated from her breastfeeding infant after Immigration and Customs Enforcement officers arrested her and her fiance at the same time. In the rush to find someone to care for the baby and Flores’ 8-year-old daughter, she called on their local pastor to take the children in.

In response to the Brookings findings, the Department of Homeland Security, which oversees ICE, sent an oft-repeated statement that the agency “does not separate families,” adding that parents are asked if they want to be removed with their children or instead to have them placed with a person the parent designates. DHS said this is consistent with the practices of past administrations.

However, guidelines for ICE officers encountering parents have changed. A document known as the Parental Interests Directive was given a new name under Trump — the Detained Parents Directive. Its preamble, which once instructed agents to handle immigrant parents in a way that was “humane,” has been stripped of the word.