Update at 6.40pm: Witness Rebecca Hewson said that after speaking with handlers, both horses "are shaken up with some minor scratches and a lot of dust but are alright".
"The horses were definitely spooked with one trying to go in one direction and the other going in the direction of the fence," Ms Hewson said.
"Horse events in the ring were halted immediately but I believe it was the Bad Boys II ride that spooked the horses."
She said only one of the horses jumped over the fence and the stagecoach landed about 15 metres from the jumping castle.
"One person started screaming and we all looked over," she said.
Country First Response attended the scene before NSW Ambulance and police arrived.
Update at 4.30pm: The two boys treated at Ganmain Show following a stagecoach flip were taken to Wagga Base Hospital, a NSW Ambulance spokesperson said.
Both the 11- and eight-year-old boys were in stable conditions.
The spokesperson said there were no major injuries and that the hospital visit was conducted as a precautionary measure.
Earlier: Two boys have been treated at the Ganmain Show after a stagecoach reportedly crashed near a jumping castle.
A NSW Ambulance spokesperson said they were called about 1pm today to the incident.
"Two ambulance crews responded to reports that a stagecoach had gone onto its sides," he said.
"There were two boys - an 11- and eight-year-old.
"Neither have injuries at the moment. Crews have done precautionary checks, looking to see if they're breathing okay and for any bumps and bruises."
A witness said it appeared the two horses drawing the stagecoach "got spooked and jumped the fence".
The wagon flipped and some people ended up in the jumping castle, the witness said.
He also said the incident happened around the main area of the showgrounds.
"Members of crowd raced after the horses and subdued them," he said.
"The wagon is quite damaged."
The witness also said there appeared to have been more people involved in the incident. However, NSW Ambulance said that at this stage, only the two boys have been treated at the scene.
It is unknown at this stage if the heavy horses are injured.
More to come.