The train at Cleveland Park in Spartanburg had 28 people on board when it derailed just after 1 p.m., said Spartanburg Police Captain Art Littlejohn.
"The train derailed and came off the tracks," he said. "It overturned, and the people were thrown from the train."
A 6-year-old child was killed, he said.
Initial accounts of how many people were injured remained unclear. Littlejohn said 15 children were taken by ambulance to hospitals and two more were airlifted by helicopter. Two adults also were hospitalized, he said.
Some of the injuries were serious, he said.
A spokesman for Spartanburg Regional Medical Center said his hospital alone received 19 injured people from the derailment. He said it was his understanding other area hospitals had also received patients.
The train ride opened for the day at noon, Littlejohn said. The train and tracks had been inspected on Wednesday, he said.
The tracks of the miniature train at Cleveland Park, which is operated by the Spartanburg County Parks Commission, circle the park's playground area.