All three were declared dead at the scene.
Other children in the taxi sustained minor to moderate injuries.
“The patients were treated for their injuries and were thereafter transported to nearby hospitals. The details surrounding this incident are not yet known. Local authorities were on the scene for further investigations,” ER24 said.
The Gauteng department of education said the deceased children were from Madibatlou Middle School.
The accident happened about 300m from the school.
A total of 16 children from the Gauteng province have died in tragic circumstances since the start of the school term last month.
They include Enock Mpianza, a Parktown Boys' High pupil who died on the first day of school at a grade 8 orientation camp.
Kelebogile Reuben Molopyane, a Ferndale High pupil, died last week after experiencing an epileptic seizure which led to him plunging from a balcony on the second floor at the school.