"The kids are all fine," San Francisco Unified School District spokeswoman Heidi Anderson said.
The district is still investigating the incident, Anderson said.
The Martin Luther King Jr. Academic Middle School children, boys and girls all between the ages of 10 and 12, found the poison atop a high filing cabinet in a classroom, according to the fire department.
The school is located at 350 Girard St. in the city's Portola District.
A concerned parent got a phone call from his daughter saying she and her friends had eaten the rat poison, according to the fire department. The incident was reported at 12:08 p.m.
Fire Department spokeswoman Lt. Mindy Talmadge said Thursday the children had apparently mistaken the poison for candy, and that two of them ingested it, while the others simply licked it.
None of the students showed any symptoms of poisoning, but were hospitalized as a precaution, Talmadge said.