The women appeared in digital images but were not seen "actively engaged" in sexually abusing the child, the FBI said.
The pair, dubbed by the FBI as Jane Doe 25 and Jane 26, may be able to help investigators determine the identity of the victim, federal authorities said.
"The victim is believed to be a young child enduring abuse currently and over the past several years by an unidentified male," the FBI said in a statement.
The child was wearing a red San Bernardino County junior fire marshal's hat.
Jane Doe 25 is described as white and between 18 and 25 years old. She has dark hair and a wing tattooed across her back, the FBI said. Jane Doe 26 is believed to Latina with dark hair and brown eyes. She is between 25 and 35 years old.