Ryan and Katie Moi spotted the blue bank deposit bag lying in the street as they were driving Monday, The (Eugene) Register-Guard reported.
Katie said she pulled over and Ryan jumped out to retrieve the bag.
"Our hearts were racing," Ryan said. "We couldn't believe it."
"Obviously, we couldn't keep it," Katie said. "When I had my laptop stolen, that was the worst feeling. I would not do that to someone else."
The siblings said they brought the bag to their dad's home for advice. Their father, Erik, said he immediately noticed paperwork enclosed in the bag showing that the money belonged to Reliable Credit, a firm that provides direct loans to people.
Ryan and Katie told their father they wished to return the bag and Erik volunteered to take care of it.
"They were dumbstruck," he said in reference to employees at Reliable Credit.
Lee Holzman, president of Reliable Credit, confirmed the story, but declined to comment on any details of the story.
"The cool part of the story is the kids and what they did," he said. "I've instructed our manager to talk with their dad and find out what would be appropriate to show our appreciation."