Police said Henry W. Bartle, 18, had left the "shotgun laying on his lap with the muzzle pointed in the direction of the child" when he attempted to get up. The 12-gauge weapon fired as Bartle stood and the tot was struck in his upper body, according to Rome police.
Bartle, who lives with the child's mother, had earlier cleaned and then loaded the shotgun, officials said.
He has been charged with criminally negligent homicide.
Shamar Walters is a reporter for NBC News' Social Newsgathering team based in New York City.