"Our family's hearts go out very strongly to the man who had this accident, and that's what we believe it was; it was an accident. These things happen," said Renee Starr, grandmother of the children.
Authorities say 9-year-old Ashlyn Gardner and her 7-year-old brother were walking in a crosswalk eastbound on Banyan Street from Etiwanda Colony Elementary School at about 3 p.m. Wednesday when they were hit by a Ford F-350.
The victims were rushed to a local hospital, where Ashlyn died a short time later. The boy was treated for moderate injuries.
The driver, identified only as a 69-year-old man, told police that he was making a left turn to head south on East Avenue, and simply did not see the children.
Ashlyn's parents and other family gathered at the site of the accident on Thursday afternoon. A makeshift memorial continues to grow, as residents stop by to leave flowers, candles, balloons and stuffed animals.
"She's always been precious. She's always been one of those kids that was good," Starr said.
The tragedy has many parents calling on the school district to take measures to prevent this from happening again.
"They need to put another crossing guard on this corner immediately," said parent Andrea Nelson. "There's a lot of traffic on this street, and there's hundreds of students walking."
Crossing guard Michelle Esler urged drivers to be responsible behind the wheel.
"These big trucks, they don't see us, and these cars are not slowing down, and numerous times a week, I almost get hit," she said.
Parents say they are going to put together a petition with the hopes that the district will resume busing to alleviate some of the traffic.
The driver was not cited, but investigators say they are still trying to determine the exact cause of the accident. Anyone who witnessed the collision is urged to call the Rancho Cucamonga Police Traffic Unit at (909) 477-2800.