The teacher, identified only by the surname Wang, is believed to have added sodium nitrite into her pupils' food, Jiaozuo city police said.
The children were reportedly taken to hospital. Most were discharged, but one had serious symptoms, according to state news agency Xinhua.
Overexposure to sodium nitrite can be toxic and possibly fatal.
Police said they were still looking for a motive.
Nursery school age in China is usually between three and six years old.
Schoolchildren in China have been the target of often fatal attacks by people bearing grudges or considered mentally ill.
In 2002, 42 people, mostly schoolchildren, died after eating snacks laced with rat poison in the eastern city of Nanjing.
The killer, who apparently was jealous of his rivals’ thriving business, was swiftly sentenced to death and executed.
Associated Press contributed to this report
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