The mother of the three-and-a-half-year-old girl, a resident of Bhagatpura Colony, lodged a complaint at the Civil Lines police station, alleging that her daughter was sexually assaulted by the neighbour when she was not at home.
When the complainant returned home after work, she found her daughter crying. Later the girl narrated the story to her mother.
The minor was taken to a hospital where she underwent a medical test, sub-inspector of police Vikram said.
Police have registered a case, the police officer said, adding that the accused would be arrested soon.