Skowhegan police said they responded to Indian Ridge Apartments Thursday night and found a two-year-old girl with serious injuries.
She was brought to the hospital, and at last check is in stable condition.
Her mother originally told police the young girl fell down the stairs, but investigators later charged 25-year-old Cody Swanson.
Investigators said Swanson knows the girl's mother and caused her injuries.
Swanson was arrested Friday night and is charged with aggravated assault. He remains behind bars.