Tomas Jay Henio's three younger brothers all have been placed with the tribe's social services department, Ramah Navajo Police Chief Emil Radosevich confirmed Monday.
"Both of the parents were intoxicated, so that's why we charged them with endangerment. We did that for the safety of the children," the police chief said.
Tomas was found Dec. 26 by his parents—stepfather Keith Comosona and mother Yolanda Henio—near their home in the community of Pinehill. They thought he was being cared for at a relative's home, but he had actually been playing in the snow alone.
They told authorities that the boy was attacked and killed by a pack of dogs. No screams or barks were heard that would have alerted them to the attack, they said.
The family dog and eight strays were rounded up and euthanized, but authorities on Monday said they were awaiting autopsy results to determine exactly how the boy died.
FBI spokesman Frank Fisher said results were expected by the end of the month and that it would be premature to talk about what federal criminal charges, if any, might apply.
Radosevich said fatal maulings aren't common on the reservation, but authorities aren't sure if that's what happened that December evening. Federal investigators were working on developing a time line, he said.
"We just have to wait and see. We don't know until the experts can give us some information," Radosevich said.
As for the tribal charges, the Ramah police chief said the parents were arrested Dec. 27 and released pending a hearing in tribal court sometime in January. It wasn't immediately clear if they had an attorney, and there was no telephone listing for them in the Pinehill area.
A breath-alcohol test conducted hours after the family first called authorities showed Comosona at 0.09 percent, just over New Mexico's legal limit of intoxication. Radosevich said the mother refused to take a test.
The chief acknowledged that many cases in the Ramah area stem from alcohol use.
The Navajo Nation, like many reservations, also has long had a problem with roaming stray, feral and neglected dogs.
After a 55-year-old man was found mauled to death two years ago in a small community near Gallup, a Navajo official in 2011 estimated there were four to five dogs for each of the more than 89,000 households. That's as many as 445,000 dogs, most of which roam free, killing livestock and biting people with alarming frequency.