Walker remains jailed on a $1 million bond. Court records did not list an attorney for her.
She also has a 3-year-old son who has been placed in foster care by CPS, agency spokeswoman Gwen Carter said.
Coleman said Walker banged the 6-month-old's head on June 20 but didn't call for medical help. He said someone called 911 early the next day, and an ambulance was sent to Walker's Angleton home. The baby died at a hospital and police began their investigation.
Coleman would not say who made the 911 call. He said investigators learned the child had suffered head trauma after talking to Walker.
"She confessed she started the abuse when he was 4 months old," the sergeant said.
Angleton police arrested Walker on a charge of injury to a child on July 26. She has been jailed since then.
Walker is now at least 10 weeks pregnant. Coleman said jail officials are monitoring her closely.
He said Walker showed "no real emotions" when telling investigators about her sons' deaths.