"We've been working a horrific scene here," Burleson told reporters gathered near the rural site on a two-lane road.
Crews had been searching for the children since Sunday afternoon, when one of their fathers called 911 to report the collapse. Officials were on the scene within minutes but couldn't get to the children.
Neighbors have said a man building the home had been digging with a backhoe earlier in the day. Lincoln County Sheriff David Carpenter would not say what was being built at the site or if the man was doing it alone or had professional help.
Burleson described the pit as 20 feet by 20 feet with a sloped entrance leading down to the 24-foot bottom. Carpenter said the children were at the bottom of the pit retrieving a child-sized pickaxe when the walls fell in on them.
Carpenter said his deputies would continue to investigate what happened. The children's names have not been released, but Carpenter said it was the boy's father who called 911.