DS1 is 4.5 and just getting into longer stories at bedtime. Recently, he's moved on from three short picture books at bedtime to chapter-length stories about the same character but not chapters, IYSWIM, since each story is self-contained. It doesn't really require him to hold in his mind where the story is up to. He also prefers stories with lots of pictures and can get a little bit glazed over if there isn't a picture on each page.
I was wondering if we should try him on some classic chapter books, like Charlie, or maybe Fantastic Mr Fox to start with. How old were your DC when you started this?