Yet Mirian, a Honduran woman who arrived in the U.S., broke no law. She simply followed the established procedure by presenting herself at an official border crossing point and requesting asylum because her life was in danger in Honduras — nevertheless, her 18-month-old was taken from her.

“The immigration officers made me walk out with my son to a government vehicle and place my son in a car seat in the vehicle,” Mirian said in a declaration accompanying the A.C.L.U. suit. “My son was crying as I put him in the seat. I did not even have a chance to comfort my son, because the officers slammed the door shut as soon as he was in his seat.”

Likewise, Ms. G, a Mexican in the A.C.L.U. suit, went to an official border crossing point and requested asylum with her 4-year-old son and blind 6-year-old daughter. None of them had broken American law, yet the children were taken from their mother.

“I have not seen my children for one and a half months,” Ms. G wrote in her declaration. “I worry about them constantly and don’t know when I will see them.”

Granted, this does not happen to all who present themselves at the border and do not cross illegally; it seems arbitrary. But even for those parents who commit a misdemeanor by illegally entering the U.S. — because they want to protect their children from Central American gangs — the United States response seems to be in effect to kidnap youngsters.

If you or I commit a misdemeanor, we might lose our kids for a few days while we’re in jail, and then we’d get them back. But border-crossers serve a few days in jail for illegal entry — and after emerging from criminal custody, they still don’t get their kids back soon, said Lee Gelernt, an A.C.L.U. lawyer. In one case, he said, it has been eight months and the child still has not been returned.

It’s true that immigration policy is a nightmare, we can’t take everyone and almost no one advocates open borders. Some immigrants bring small children with them and claim to be the parent in hopes that this will spare them from detention.