The Coffee County Sheriff’s Department said the toddler shot the infant with a .25-caliber automatic pistol in a home Tuesday afternoon in the community of Hillsboro, which is about 70 miles southeast of Nashville.
The 18-month-old was transported to a local hospital. His condition is unknown.
Sgt. Danny Ferrell told the Associated Press that investigators are still trying to determine how the child was able to get a hold of the weapon. He said the 3-year-old was not harmed.
Authorities are not identifying the boys.