The incident happened around 2:15 p.m. Sunday at the Oyster Festival at Veterans Memorial Park in Norwalk.
The popular festival was packed with visitors thanks to the nice weather, and the Zumur swing ride was nearly full at the time of the accident.
The mechanical failure caused the ride to suddenly stop, sending the swinging riders careening into each other.
A panic ensued as parents tried to get to their kids.
"I head a big bang, and the whole apparatus, the swings, came smashing down to the bottom of the swing," dad Ron Lasky said. "And it just kept spinning around. The kid who was running the ride was asking, 'Oh my gosh, what just happened? What just happened?' as I already ran in and knocked down the fence so other parents could get in and start taking their kids off. I removed a couple of kids, but it seemed like they had no plan for something bad happening."
State police investigators determined that an internal component failure in the area of the transmission involving seizure of bearings caused the ride to stop suddenly.
The ride had been subject to regular inspections.
The ride will be taken apart in an effort to determine what caused the accident, the ride's owner said Monday.
Connecticut state police said the owner, Stewart Amusement Co. in Monroe, Conn., has no history of safety violations.
And an official with the successor company of the ride's manufacturer said he wasn't aware of any previous similar problems involving the Zumur ride.
A total of 13 people, including 12 children, were taken to the hospital. Only one, an 8-year-old boy, remains there. Two other people refused treatment at the scene, police said.
The festival's organizer, the nonprofit Norwalk Seaport Association, said it directed the ride's operator, Stewart Amusement, to shut down the entire ride area until state inspectors completed a check. The other rides later reopened and the rest of the festival remained open on its third and final day.
As of Monday morning, the rides have all been disassembled and only a few tents remain.