A total of 27 children from a kindergarten in Songjiang District left hospitals yesterday after treatment for suspected food poisoning.
The children, aged five and six, had been taken for treatment the previous day after eating dumplings made in the kindergarten's canteen.
Two were sent to hospital by the kindergarten staff at 4pm on Wednesday, while more were taken by their parents later that evening.
The children were treated at three hospitals - Minhang District Central Hospital, Children's Hospital of Fudan University and Songjiang District Central Hospital.
An official at the Minhang hospital said most of the children had mild food-poisoning-like symptoms.
About 80 percent of food-poisoning cases are bacterial ones, while this one looked like a viral infection as most children didn't have fever, according to Gu Zhenhua, an official from the Shanghai Food and Drug Administration.
The FDA is investigating the cause, and food samples from the Xinqiao County Central Kindergarten have been sent for testing.
It will take two to three days to get results.
Kindergarten officials suspect that the dumplings served at the canteen may have been to blame.
All the children had eaten dumplings made and served by canteen staff at lunch on Wednesday, said the kindergarten's director, a woman surnamed Zhuang.
The kindergarten was open as normal yesterday, but its canteen is closed while the investigation is ongoing.
Danger all in a day's work for engineer