Police are not treating the death as suspicious.
It is believed the boy and his grandparents arrived shortly before the tragedy and were renting the caravan locally. The owner of the park arrived at the scene around 2pm yesterday with a police inspector but declined to comment.
Later it emerged that the youngster's grandparents, who have not been named, are in Stracathro Hospital in Brechin.
The grandmother was taken there with a suspected stroke. Her husband was also taken to hospital when he suffered a heart attack after his grandson's body was discovered. The family had been intending to stay in the caravan over the Easter weekend.
Health and Safety Executive inspectors were at the scene. A spokesman said: "The ... executive are investigating and will submit a report to the Procurator Fiscal."