The unmarried parents, 18 and 19 years old, are accused in the alleged 6-week-old assault that officials at McKenzie, Tenn., Regional Hospital said they discovered during a prerelease examination of the child.
"Based on the investigation, we ruled out everyone but the mom and the dad," McKenzie Police Lt. Tim Nanney told the Jackson (Tenn.) Sun.
The infant's father was being held on $100,000 bond while the mother was being held on $5,000 bond.
The mother also was charged in the sexual assault because, "I could not exclude her from being part of it," Nanney said.
The infant has been placed with a relative and neither parent is allowed to see her.
The newspaper did not name the parents, citing its policy of not identifying sexual assault victims.