But many parents who were deported without their children, like Mr. Domingo, have found that instead of speeding things up, leaving the United States has only delayed reunification. They often don’t understand the cumbersome legal process in which their children are trapped, or know when they might be with them again — uncertainty that leaves them anguished.

“It’s been enough pain,” Mr. Domingo said. “How much more does the government want us to suffer? It’s too much.”

The American authorities decline to comment on individual cases involving minors.

Last month, under orders from Judge Dana M. Sabraw of Federal District Court in Southern California, the government submitted a strategy to reunify children with parents who had been deported. Its details were ironed out in conference with the American Civil Liberties Union, which filed a suit against the government over the separation policy.

Under the plan, the government has designated officials in various departments to steer its efforts and is coordinating with Central American consular officials in the United States to prepare the children’s travel documents. The government has also assumed financial responsibility for repatriating the children.

But locating the parents in their countries of origin and identifying their children within the immigration bureaucracy is difficult. That burden has fallen to a coalition of American advocacy groups that have taken on the task in the hope of speeding up the process.

“The A.C.L.U., private firms and N.G.O.s are largely doing what the government should be doing,” said Lee Gelernt, the lead A.C.L.U. lawyer in the case. “Is that ideal for all of us? No. Is it necessary? Yes.”