XI'AN, March 15 -- For the past several days, life has been awash with anxiety, despair and anger for the hundreds of parents whose children attended two kindergartens caught in an antiviral drug scandal.

The Hongji Xincheng and Fengyun kindergartens in Xi'an City, capital of northwest China's Shaanxi Province, are accused of having administered antiviral drugs to children since 2008, local authorities announced on Thursday. The two kindergartens have a total of 1455 kids.

One of the parents, who only gave his surname as Zhang, said that his child previously attended the Fengyun kindergarten and had developed symptoms of dizziness, stomachache, leg pains and genital swelling since 2013.

"I thought my child was only suffering from cold, only to find that he was given moroxydine ABOB," said Zhang.

Zhang's ire was shared by another parent, surnamed Yang, whose five-year-old daughter was attending the Hongji Xincheng kindergarten, only two kilometers away from Fengyun.

Yang's daughter told her that the teacher gave the whole class "blue pills" at noon every day, adding that it was a "secret" between her and the teacher.

On the heels of the shocking discovery, scores of angry parents blocked a road near the two kindergartens on Wednesday, demanding local government's intervention in the case.

Local police later detained the private Fengyun kindergarten's legal representative, surnamed Sun, its principal, surnamed Zhao, and kindergarten doctor, surnamed Huang, on Wednesday. On Thursday, two other suspects, the deputy principal of Hongji Xincheng kindergarten, surnamed Zhao, and the kindergarten doctor, were detained on suspicions of medical malpractice.

This scandal is just another in a string of cases related to the mishandling of children in China that has tainted the country's education system.

In 2013, a 62-year-old primary school teacher in east China's Jiangxi Province was sentenced to 14 years in jail in October for molesting seven second-grade girls in class and infecting six of them with STDs.

In the same month, a two-year-old boy was left unattended on a school bus for more than half a day in central China's Hubei Province. The child died in a hospital later that day.

The latest headline story attracted the attention of parents and experts alike, with many lashing China's education system, which is marred by a spate of flaws that threaten the safety of children.

Ms. Zhu, whose three-year-old son attends a privately run kindergarten in Xi'an, chided the educational institutions for their mistreatment of children.

"How could they be so ignorant and apathetic toward the chubby-cheeked children?" Zhu said.

Zhu said that she could not sleep for two consecutive nights following the incident, worrying that other kindergartens in the city might have similar practices.

Zhu said that the government should ramp up transparency and supervision of kindergartens to ease the minds of concerned parents.

While children's safety is a big concern, others have raised doubts about the credibility of renowned non-governmental organizations (NGOs), as both the kindergartens have claimed they are affiliated with the China Soong Ching Ling Foundation, a well-known NGO named after the wife of Dr. Sun Yat-sen.

Zhang Ying, deputy secretary-general of the foundation, admitted that the two kindergartens were affiliated with the foundation, but denied any economic contact or business cooperation with them.

But parents of the victims said that they sent their children to the kindergartens only because they trusted the foundation, and they cautioned that the NGO should not shirk responsibility in the ordeal.

The parents pointed out that the illegal behavior, which was not spotted by any government body over the past six years, reflected the wider and increasingly urgent problem of a lack of sufficient government supervision that is playing out in China's private education institutions.

Guo Bing, executive director of Zhen'Ai Education Service Organization, an education NGO in Beijing, said that some education institutions are over-commercialized at the moment, and children's safety, which should have been a top priority, is largely left behind.

"Some budget-minded owners of private kindergartens spend little on the training of teachers and provide low teaching salaries, forcing many teachers to unleash their pressure on children and causing safety concerns," Guo said.

Guo added that China needs to step up laws and regulations to strengthen supervision amid mounting public scrutiny toward the education system, while stiff penalties should be meted out for those who violate the laws.

As of Friday, order had been restored at the two kindergartens. More than 200 children have received free physical examinations since Wednesday, while the city's education department has carried out safety examinations at all kindergartens and schools in Xi'an.

A parent whose child just returned to Fengyun said that the government should learn a lesson to avoid similar cases.

"I hope that things like this will never happen again," said the parent, who declined to give her real name.