A private kindergarten in Xi'an, capital of Shaanxi province, is being investigated after allegations that it gave children unauthorized prescription medicine.

Three school officials were detained by the police.

According to Huang Xiaohua, deputy secretary-general of the Xi'an municipal government, a joint investigation team from the city's education bureau, health bureau, food and medicine administration and public security bureau has been sent to the Feng Yun Kindergarten.

Sun Xuehong, the school's owner; Zhao Baoying, the manager; and Huang Linxia, the care physician, were all detained by the police, Huang said.

The 690 children attending the kindergarten were sent to a local hospital for health examinations on Wednesday, and those who were affected by the medicine would be treated, Huang said.

A mother surnamed Cheng discovered by chance that her 5-year-old daughter had taken a tablet of guanidine hydrochloride, a prescription anti-viral drug that should be given only by qualified doctors.

She wrote about the incident on her micro blog, creating a stir among parents of children who also attended the kindergarten.

"My daughter told me she took the medicine in the kindergarten on March 6, and I wondered why the kindergarten gave her the tablets, since she was not ill," Cheng said.

Guanidine hydrochloride is used to treat viral influenza or herpes virus infections and can have side effects, including sweating, loss of appetite and low blood sugar.

"The kindergarten never told us parents that they gave our kids that medicine, and we want to know why they did this," another mother, surnamed Wang, said.

On Tuesday, Li Na, the mother of a 7-year-old boy, went to the kindergarten for an explanation. The child, who has been enrolled in the kindergarten since 2010, had suffered a "strange, long-term stomachache", and Li couldn't find the cause. A health examination showed that the boy had hydronephrosis, a serious kidney condition, Xinmin Weekly reported.

Many other parents said their children had itchy skin and night sweats. A mother surnamed Wu said her daughter suddenly woke up one night last week with hair so wet that looked as though it had just been washed, the report said.

The preliminary investigation showed that the kindergarten started giving the medicine to the children last March, and the care physician was not a qualified doctor authorized to dispense prescription drugs.

The kindergarten's manager, Zhao Baoying, said the medicine was used to prevent colds, the authorities said. But Hou Wei, a pediatrics professor at a local hospital, said that the medicine is for curing, not prevention.

"I suspect they gave the medicine to our kids for money, because the agreement signed between us and the kindergarten says that a week's worth of fees would be refunded if a child stays sick at home for three days, and a month's fee if a child stays sick at home for 10 days," Cheng, the mother, said.

She said she found that the medicine is cheap, selling for 1.5 yuan (24 cents) per bottle of 100 tablets.

Wang Naiming, deputy director of the education bureau of the city's Lianhu district, which has jurisdiction over the kindergarten, said the government has sent a new manager and 24 nursery teachers from other kindergartens to help run it for now.

The local government provided all 690 children with a health examination at no charge.

Huang Xiaohua, the city's deputy secretary-general, said that the assets of the kindergarten have been frozen and the children's parents could ask for compensation.