The children were ages 5 and 9, the tribe said. Their names were not immediately released.
Tribal police and emergency responders received a call about 4:30 p.m. Sunday that two children had fallen through the ice on a pond on Old Agency Loop Road in Plummer, the tribe said.
"They were found by their grandmother, who called 911 and then pulled them out of the pond," the tribe said in a news release. "Early reports indicate the children may have been looking for their dog when they fell through the ice."
The children were taken by ambulance to Kootenai Medical Center in nearby Coeur d'Alene, Idaho.
The Kootenai County Coroner's Office will conduct autopsies to determine the cause of death, the tribe said.
Plummer is a small town about 45 miles southeast of Spokane, Wash, near the Washington-Idaho border.