On Wednesday, two couples — Amos and Ruth River, and Timothy and Victoria River — were arrested while driving away from the Fence Lake compound. Eleven children, ages 4 to 17, were in their vans, the authorities said.

The two couples were charged with failure to report the birth of their children and pleaded not guilty. They were being held on bond.

Robert Lohbeck, a lawyer for the four River defendants, said they had been arrested while driving with the children to his Albuquerque office after speaking with him by telephone to retain his services. He said the couples had agreed to undergo DNA testing and other procedures to obtain birth certificates for the children.

“We are dealing with very unsophisticated folks — they live in an area that is a fairly isolated area,” Mr. Lohbeck said in a telephone interview. “Most people did not know or would not realize it is a felony crime to not register birth. My clients had no idea that it was some kind of legal requirement. Ultimately this will all be cleared up administratively.”

The children are being interviewed by the F.B.I. this week, Sheriff Mace said. An F.B.I. spokesman referred calls to the sheriff’s office.

New Mexico’s attorney general, Hector H. Balderas Jr., said in an emailed statement on Friday that his office was working with the state’s Children, Youth and Families Department and the district attorney to evaluate whether human trafficking and abuse had occurred.

Sheriff Mace said he did not know exactly how many people were members of the sect. He added that many of the members had assumed biblical names and aliases and that their birth dates were not always possible to verify.