The Pierce County prosecutor filed the charge Thursday against 28-year-old Derrick Myers. He lived with the mother of Terric Davis and was alone with him Tuesday while she was at work.
She found the boy sick when she returned home and took him to Mary Bridge Children's Hospital where he died.
The prosecutor's office says the attending physician told police that it was a case of child abuse. An autopsy determined Terric died of blows to the abdomen. He had injuries to his pancreas and bowel, also a skull fracture and numerous bruises.
Myers is being held on $2 million bail.