Alivia Stahl, 9, and her brothers, Xzavier and Mason Ingle, were killed on Tuesday morning as they crossed the street to board their waiting school bus.
The siblings' uncle, Elgin Ingle, said it appeared as though Alivia had tried to step in front of the boys to protect them.
"It's horrible that this happened," Ingle said. "They were holding hands every day on the way to the bus stop, including today … it looks like Alivia stepped in front of the car for the boys.
"It looks like Alivia seen what was happening, and she stepped up like a hero. I wish she could've saved her brothers, but she's still a hero."
Another boy, 11-year-old Maverik Lowe, was seriously injured in the crash. So far, he's undergone three surgeries, his mother said, and has a long recovery ahead.
The driver of the car that hit them, 24-year-old Alyssa Shepherd, has been charged with three counts of reckless homicide as well as a misdemeanor for passing a stopped school bus. She has been released on $15,000 bond and has not yet entered a plea.
National Transportation Safety Board investigators are looking into what led to the crash.
According to CBS News, one estimate stated that more than 15 million Americans pass stopped school buses each year, at a rate of 85,000 times every school day, despite the fact that doing so is illegal in all 50 states.