Police said the mother, whose identity was not released, claims she left her daughter at a Chuck E. Cheese's Pizza restaurant because she thought the girl was spending the night with her aunt, the Chicago Tribune said Sunday.
The girl's aunt also departed the restaurant with the belief the girl was staying with her mother for the night, police said.
The young girl was found alone at the eatery Saturday night after the adults both departed and her picture was posted online to find family members.
The aunt, whose identity was also not released, saw the online photo Sunday morning and contacted the girl's mother regarding the mix-up, the report said.
The Tribune said the girl is in the custody of the Illinois Department of Children and Family Services, while authorities determine whether any criminal charges will be filed in the matter.