An 11-year-old girl stabbed a 12-year-old boy inside their Bronx middle school Monday – minutes before a pre-teen unleashed pepper spray in his Queens school’s cafeteria, sending two kids to the hospital, cops and sources said.

The girl allegedly slashed the boy in the left arm with a kitchen knife minutes after 11 a.m. inside IS 218 on Gerard Avenue near East 167th Street in Concourse, authorities and sources said.

The young victim was taken to Lincoln Medical Center, where he was listed in stable condition.

His assailant was taken into custody, the sources said.

The violence stemmed from a “past incident” that boiled over between the two middle schoolers, the sources said.

The school does not have metal detectors installed, and only has one school safety agent for its 800 students, sources added.

Across the city, in an unrelated incident around 11:20 a.m., an 11-year-old student released pepper spray in the cafeteria of JHS 217 on 144th Street in Briarwood, police and sources said.

About 100 students were having lunch in the room at the time, cops said.

Two 12-year-old students – one boy and one girl – were taken to the Elmhurst Hospital Center for treatment, cops said.

Two students were taken into custody and the pepper spray was recovered, police said.

The school is part of a campus that has a student population of about 1,300, with only three school safety agents assigned, the sources said.