A witness told rescue officials that a Ferris wheel cart flopped upside down, ejecting the three people.
Officials said the injuries to the boy and to another woman weren't life-threatening.
The three were rushed to Harbor View Medical Center in Seattle after the acident at the Rhododendron carnival in Port Townsend, reported CBS News.
A malfunction apparently caused the cart they were riding in to flip, causing them to fall 15 to 18 feet onto the ride's metal platform.
People on the scene said it appeared a pin or section came off the wheel, but it's unclear what exactly fell out from the ride.
The incident occurred at the Rhododendron Festival in Port Townsend at approximately 6pm local time yesterday. The other people fell on her, ' Mr Beezley said.
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The riders who fell - a 59-year-old woman, a 47-year-old woman, and a 7-year-old boy - were taken to hospitals. "It took a few seconds for the ride operator to stop the ride".
Responders were told the cart was faulty, and the after-hour's number for the State Department of Labor and Industries was called. Private amusement ride inspectors do annual safety inspections.
The accident happened around 6:30 p.m.at the Rhododendron Festival.
The festival says authorities and the company that owns the carnival equipment are investigating.
The festival posted a statement on its Facebook page thanking "all the volunteers and employees that stepped up out of the crowd to make sure the victims were attended to and the incident was controlled".