An investigation which began April 26 revealed the 15-month-old child suffered a head injury while being babysat by the suspect, 37-year-old Heather Greenman.
Greenman told authorities the child fell while running at home in the 14200 block of Barolo Way in Beaumont.
The child was taken to the hospital for treatment of "swelling of the head and bleeding on the brain" but was later pronounced dead.
Authorities were able to locate a second victim, a 2-year-old child, who had suffered from several serious injuries while in Greeman's care but were not previously reported, officials said.
The child was also being cared for in the family's home in Beaumont but was not hospitalized.
Detectives believe there may be additional victims.
Anyone with information is asked to call Beaumont Police Department Detective Sergeant at 951-769-8500. Information can also be reported anonymously at firstname.lastname@example.org.