The incident occurred on Thursday at the Gyandeep Shishu Mandir in the Harduaganj area.
An initial probe found that the biscuits were well past the expiry date, printed on the package, Circle Officer (CO) Qwarsi M.K. Saxena said. A case of carelessness was registered against the school management, he said.
Police said that the biscuit packets were distributed to the children soon after the flag hoisting ceremony in the school. Some children started vomiting and complained of stomach ache.
As the news spread, police and concerned parents rushed to the school and the children were taken to a nearby medical facility.
All the children were discharged from the Pandit Deendayal Upadhyaya Hospital after about an hour.