The dead victims -- all from two families -- were asleep when the fire broke out, ravaging their tent close to an island beach near the western city of Incheon.
"The tent was completely gutted within a minute," Ryoo Hwan-Hyeong, head of the Ganghwa Island fire station, told journalists.
An investigation was underway to determine the cause of the blaze, but firefighters suspect a short circuit in the victims' electric sleeping mat may have triggered the fire.
The two injured included a 43-year-old man surnamed Park, who was sleeping in another tent nearby.
The boy suffered burn injuries and Park was being treated for smoke inhalation.
