The small child wandered off and the mother did not appear to be concerned Riverside Police officials said.
Riverside police identified the woman as 31-year-old Chiengkham Vilaysane.
"We just want to talk to her to really start figuring out what's going on, especially to make sure she's OK as well", he said.
Detectives are asking for the public's help in identifying the woman.
Vilaysane was caught on surveillance video entering the store in the 4200 block of Van Buren Boulevard Sunday with the toddler by her side.
Colby Dee Mattsson was on the clock Sunday night at Food for Less in Riverside and noticed the mother and daughter in the store. "The mother deserted the toddler after she paid for the groceries".
Officers were called to the store when the child was found alone.
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The child was placed in protective custody by Child Protective Services.
The mother reportedly keep shopping and was approached by a good Samaritan who brought the child back to her.
"It appears the toddler was intentionally left in the store by the mother", according to Riverside police.
The young girl identified the woman as her "mommy" when she was shown a photo from surveillance footage, according to police.
The child was not with her. She could face allegations of felony child endangerment or abandonment.
As of Monday, no one had reported the girl missing and the mother had not yet been located. It's not known who the father of the abandoned child is, he added.