Linda Maddox, 63, was asleep at home alone with her twin grandsons in Town 'n' Country, near Tampa, while the boys' father went to work Sunday night.
Maddox had placed a chair against the bedroom door handle for extra protection. When she awoke around 1 a.m. to the sound of the chair scraping on the wood floor, she grabbed the loaded .22-caliber revolver she keeps by the bed and fired off a shot.
Seconds later, Maddox realized her mistake: Instead of a would-be burglar, she had shot her grandson, Tyler.
Tyler was transported to St. Joseph's hospital, where he remains in critical but stable condition, Hillsborough County Sheriffs said.
The shooting is under investigation.