The bus, taking students to the Newport Elementary School, was knocked on its side, its windows shattered, after it collided with a Jeep Wrangler and a Jeep Cherokee at an intersection in Newport Township near Wadsworth, the Chicago Tribune reported.
The driver of the Wrangler was killed. The 12 injured children were taken to a hospital for treatment of injuries, with one student said to have one or more broken bones.
Lake County Sheriff Mark Curran, citing witness reports, said the bus "may have been late on the light."
Curran described the bus driver as "coherent, obviously upset" and said she would be tested for drugs and alcohol, which is routine in a fatal accident.
Twenty-three children were determined to be in good to fair condition and were taken to a hospital aboard another bus, accompanied by paramedics.
Two people in the Cherokee were taken to the hospital.