Tacoma police spokesman Mark Fulghum said the boy's mother called 911 at about 7 a.m. Friday and said she had killed her child.
Officers and medics responded to her home, in the 3600 block of South Thompson, where they found the little boy, Noah Walker, 2. He was transported to Mary Bridge Children's Hospital, where he was pronounced dead.
The mother was later identified by the Pierce County Medical Examiner as Aleesha M. Walker, 28.
Aleesha Walker was taken into custody, questioned and booked into the Pierce County Jail for investigation of murder. She has no other children.
Records show Walker has a history of criminal misdemeanor offenses, including fourth-degree assault and solicitation for prostitution.
But there are no child abuse arrests and neighbors say they saw no signs of trouble.
"She seemed fine to me - like a normal person," said Lisa Portillo. "Couldn't imagine her doing anything to hurt her child."
But just after Noah was born, a woman said she reported Walker to Child Protective Services.
"CPS was well aware of the risk and didn't do anything and now we have a little innocent baby that died today," Deborah Dahl said.
CPS wouldn't comment on any investigation of Walker, other than to say allegations of abuse or neglect weren't founded - meaning they couldn't substantiate Dahl's claim.
Walker is being held in jail without bail. Her next scheduled court appearance is Monday.