The removal of three children with U.S. citizenship with their families to Honduras last week has prompted alarm that President Trump’s strict immigration enforcement may have crossed “illegal and unconstitutional” lines, as a federal judge in one of the cases put it.

Lawyers for the two families involved said the mothers were not given an option to leave their children in the United States before they were deported. But Mr. Trump’s border czar, Tom Homan, said the mothers requested the children’s removal.

The cases have added to growing concerns that the Trump administration may be violating the Constitution in its increasingly stringent crackdown on immigration, including removing U.S. citizens, a desire that Mr. Trump has expressed in the past but that legal experts say runs against longstanding prohibitions.

Here is a look at the cases and what is at stake.

What happened?

Three children who are U.S. citizens were removed to Honduras last week as part of the deportation of other members of their families.

Two of the children, ages 4 and 7, belong to one Honduran family. The mother of those children had an outstanding deportation order and had shown up to an Immigration and Customs Enforcement check-in on Thursday, said Gracie Willis, the raids response coordinator with the National Immigration Project, who is helping the family’s immigration lawyer with the case.

The 4-year-old, Ms. Willis said, has cancer. The mother had shown up to the check-in with a lawyer but was quickly thrust into the deportation process. Her lawyer had no meaningful chance to try to stop the deportation in court, Ms. Willis said.