Deputies and medics responded to the scene, in the 200 block of NE Madrona Ave in Belfair, at about 11:30 a.m. after receiving a report that the boy was unconscious after slipping and falling, said Mason County Chief Deputy Dean Byrd.
The boy was airlifted to Harborview Medical Center in Seattle, where he is listed in critical condition.
"We are currently investigating to see exactly what happened," Byrd said. "The circumstances are suspicious enough that we feel an investigation is appropriate."
He said the family of the young boy has had previous contact with Child Protective Services and other law enforcement agencies.
The initial focus of the investigation will be to determine whether the boy's severe injuries are consistent with the parents' account that he slipped and fell in the kitchen, Byrd said.
"We're going to be talking to the parents, we're going to be looking at the crime scene and see if things are consistent with the stories we're getting or not," he said.