MILL VALLEY, Calif. -- A 68-year-old grandmother remained in critical condition at Marin General Hospital Tuesday after she was struck by an SUV being driven by her 8-year-old grandson.

Mill Valley police said Sandra Johnson, who as visiting from Boca Raton, Florida, apparently turned the wheel over to the young boy to have him back the vehicle out of the family’s garage.

The boy apparently hit the accelerator instead of the brake on the 2008 Acura MDX and a side door crashed into the woman, knocking her to the ground.

Johnson suffered a broken vertebra, broken ribs, two broken ankles and other injuries in the accident that occurred shortly after 1 p.m. Friday. CHP spokesman Ross Ingels said there were no witnesses to the accident, which remained under investigation. Officials were unclear why the woman asked the boy to drive the vehicle. No citations have been issued.