JK Rowling has taken a major plot point of Harry Potter and the Deathly Hallows to fashion a children's book out of it. Tales of Beedle the Bard is a book in Book 7 that is bequeathed to Hermione Granger.
Using the ruse that Hermione translated the tales from ancient runes, JKR produces 5 innovative children's tales. Each one is different, most of them having macabre elements that get resolved by the end of the story in such a way that the gory bits do not seem that gory at all.
The stories still carry JKR's punch and inventiveness and are fun to read. There are just 5 tales in the book and it is a quick read. Which is why JKR has an additional section after every story under the guise of them being "notes by Albus Dumbledore". While these provide more details and extend the book, they are a deterrent to the story. The Dumbledore comments are longer than the stories and don't really add anything to the HP lore. Those that are not familiar with it will not understand the text anyway, so the purpose of these additions is perplexing. Moreover, the notes try to explain the meaning of the story which is a tad condescending to the reader since the stories are so well written the "moral" of the tale comes through pretty easily. By dumbing it down, she has actually made it worse to read.
I suspect that the publisher's insisted she have additional text in order to make it a bigger book so they could charge more for it. If that was the case, then it only served to weaken the impact of the stories. If it was just JKR's doing, then the finger that she had on a child's pulse has slipped just a little bit.
(I have intentionally not reviewed any of the tales as I'd like you to discover the stories for yourself).