More than 145,000 U.S. citizen children have likely been separated from at least one parent due to immigration detention since the start of Donald Trump's second presidency, according to a study released Monday by the Brookings Institution.

The report estimates that approximately 146,635 children who are U.S. citizens have experienced a parent being detained by immigration authorities during the mass deportation campaign that began after Trump retook office in January. Of those children, more than 22,000 experienced the detention of all their co-resident parents, the study found.

The research indicates that about 36 percent of children whose parents were detained were younger than six years old, highlighting the impact on very young children during family separations.

Separately, individual cases continue to emerge showing the human impact of immigration enforcement policies. NBC News reported on a case involving a U.S. citizen girl with a rare brain tumor whose parents were deported to Mexico. According to her family, the girl's medical condition has worsened since the deportation, and she is not receiving the specialized care she requires. The family's request for humanitarian parole to return has been denied.

The Brookings Institution study represents an attempt to quantify the scale of family separations occurring during current immigration enforcement operations, though immigration officials have not released comprehensive data on the number of children affected by recent detention and deportation activities.