While the children were playing, a plane approaching Los Angeles International Airport (LAX) dumped the fuel, which fell over the group.
The school was not named, reports KTLA5 in Los Angeles, but video from the station shows multiple first responder units, including ambulances, at the scene of Park Avenue Elementary School in Cudahy, a small city located in southeastern Los Angeles County. Students and staff may have been sprayed by fuel or inhaled fumes.
Paramedics were immediately called to treat anyone complaining of "skin irritation or breathing problems", it said.
They added: 'All minor injuries w/ no transports to local hospital from school.
Firefighters were working to confirm the nature of the substance.
The Federal Aviation Administration confirmed that Delta Flight 89 bound for Shanghai, China, declared an emergency shortly after takeoff and returned to LAX.
"UPDATE*** 70 firefighters [FF] and paramedics on-scene and committed to providing care for those injured. The aircraft landed safely after an emergency fuel release to reduce landing weight." a Delta spokesperson said.
In addition to Park Avenue, other schools in the area were also impacted by the jet fuel dump, including Jordan High School in Florence-Firestone and 93rd St.