The 20-year-old father was arrested Wednesday after his 14-day-old baby was found to have a skull fracture.
Nathan Lee Webster was booked into the Benton County jail on investigation of second-degree assault of a child.
Kennewick police Lt. Jason Kiel said in a news release that the baby's 19-year-old mother and 20-year-old father brought him to the Kadlec Freestanding Emergency Room in Kennewick about 1 p.m. Wednesday.
The baby was suffering from a skull fracture and bruising and swelling to the left side of his face, said Kiel.
"The parents told medical staff they did not know how the infant obtained the injuries," said Kiel.
Kennewick detectives spoke with the parents individually, served a search warrant at their home and arrested the dad.
The baby was flown to a hospital outside of the area and was listed in stable condition, said Kiel.