The Brookings Institution estimated that the detention of roughly 400,000 immigrants during the first 14 months of President Donald Trump's second term has separated about 145,000 American children from at least one parent. The figure exceeds the Department of Homeland Security's calculation, which placed the number of U.S. citizen children separated from a parent over the same period at about 60,000.

Since the start of Trump's second term, the administration has detained nearly half a million immigrants. The parents of the affected U.S. citizen children come from various countries, predominantly in Latin America and Central America. About one-third of those children are under age six, and the group ranges in age up to 17.

To produce its estimate, Brookings applied survey data on undocumented immigrants' likelihood of having children, based on age and marital status, to the known detainee population. "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," said Tara Watson, a senior fellow at the Brookings Institution.

U.S. Immigration and Customs Enforcement is supposed to ask detainees about their parental status, and the government produces annual statistics on the children of people who are detained or deported. Immigrants sometimes do not feel comfortable sharing information about their children for fear of further enforcement against their family.

Children who are U.S. citizens and have deported parents usually remain in the United States with friends and family. Some are placed on deportation flights to their parent's country of origin at the parent's request, even though the children are not being formally deported. In one case, a woman who was in the U.S. illegally was deported without her toddler, Orlin Hernandez Reyes, a U.S. citizen, and the child was subsequently murdered by a violent uncle.

Watson described the limits of agency responsibility for the affected children. "I think ICE isn't really in the business of child welfare. That's not their primary mission," she said. She added that the child welfare system also does not have an obligation to get involved unless there is an accusation of abuse or neglect.