A 13-year-old girl fell 10m onto concrete after ride operators failed to properly secure her restraint. She did not suffer any serious injuries.
Accidents
Theme parks and roller coasters are statistically very, very, very safe. Out of the millions of people who ride the thousands of rides every year, there are only a small handful of incidents. You are statistically more likely to be involved in an accident driving to an amusement park than having one at a park. The rarity of accidents is one reason why the media report them, similar to plane crashes.
Every important element of a ride is inspected on a regular basis and every ride is tested every day without passengers before it opens. A ride might not open, or a safety system might activate, if there is an imperfection. For theme parks to operate, they must obtain insurance and one stipulation is their rides are frequently inspected and signed off by a strict Health & Safety governing body. Every theme park does what they can to prevent accidents because the negative press would be bad for business.
Having said all that, theme park accidents still happen…
Cosmonaut, Luna Park, St. Petersburg, Russia
One of the two cables supporting the rocket “captive flying machine” style ride snapped leaving 10 riders dangling in mid-air. Source (with video)
Space Journey, Overseas Chinese Town East, Shenzhen, China
Six people died when one of the ride pods detached itself from the ride.
El Pendulo, Tibidabo, Barcelona, Spain
A 15-year-old girl died and two others were injured when the ride collapsed.
Monte Aurora, Terra Encantada, Rio De Janeiro, Brazil
A 61-year-old woman fell 30ft to her death after the restraints opened mid-ride.
Commander, Steinert Kirmes, Lüdenscheid, Germany
Ten people were injured, two seriously, when an empty gondola ripped from its swing arm and flew into the crowd of on-lookers. Source (in German)
Crazy Frog, Travelling Fair, Barnard Castle, UK
A fair worker sustained serious injuries, including a fractured skull and eye socket, after being thrown from the ride. Colleagues had failed to ensure that he was properly restrained in the ride.
Antelope, Gullivers Warrington, Cheshire, UK
A woman suffered whiplash injuries when the ride came to a halt. Source
Expedition GeForce, Holiday Park, Germany
Riders were stranded for several hours after the train derailed. No serious injuries were reported. Source (in German)
Tomorrowland Speedway, Walt Disney World, Florida, USA
A worker broke his leg when a rider crashed a go-kart. Source