The suspect, a former janitor at the school who was angry after he failed to pass his probation, used a hammer-like weapon to hit the children's skulls one by one, Hong Kong-based South China Morning Post quoted a former school maintenance worker surnamed Liang as saying.
Three of the children have serious but non-life-threatening injuries, media reports quoted police as saying.
The suspect has been brought under control, police said.
According to some reports, it was a knife attack. However, some parents said over social media that the man hit the students with a hammer-like object on their heads.
"The children were attacked while they were doing exercise on the school's running track.
"The attacker was standing nearby and used a hammer-like weapon to hit the children's skulls one by one, before he was stopped by the PE (Physical Education) teacher," the Post report quoted a parent as saying.
A doctor posted on social media: "The mayor today came to the hospital to wait with us while the children were being medically treated. We have paused several operations to save all the children".
A man has been detained on suspicion of carrying out the attack, the Post report said.
Attacks on kindergarten schools and civilians in malls by disgruntled people have become common in China lately.
In January 2017, a farmer slashed and injured 12 children with a knife at a kindergarten in Youyi town, Pingxiang city. Four children were seriously injured while eight others received minor injuries.
The attacker was executed on Friday, the Supreme People's Court said Monday.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)