While Huey, Dewey, and Louie live with Donald Duck, he is actually their uncle, not their father. So what happened to the trio's parents? Why do they live with their uncle?
Well, in one of the early comics, it was revealed that Huey, Dewey, and Louie's mother was Della Duck, Donald's sister. After they put firecrackers under their dad's chair, he ended up in the hospital and the boys were sent to stay with their uncle -- which turned into a permanent living arrangement.
No one knows what happened to Della and her husband after that. Perhaps they died? Perhaps they abandoned their kids? The world may never know.