The crash happened at the Deliverance Church at 21st and Lehigh streets, which was hosting a Head Start class at the time.
Police say the driver, an 83-year-old woman, hit the gas instead of the brakes and drove through the front glass window.
A 4-year-old suffered facial cuts, a 5-year-old suffered a foot injury and another 5-year-old was knocked down but suffered no obvious injuries. Still, all three children were taken to the hospital.
The driver was hyperventilating after the crash, police said, and was taken to the hospital to be checked out.
There were no life-threatening injuries.
Police said they are investigating but it appears to be just an accident.