It is 'what you do with it' that counts, and although JK Rowling has made no secret of her plunder of old myths and folktales, she has used these in her own way to populate the world she has created with fascinating creatures. When Tolkien created The Hobbit he too used old myths and folktales, creatures such as trolls, goblins and dragons, all such things that are guaranteed to have young readers' imaginations running wild and their eyes popping out of their heads as they hear these tales. Creatures like this are important in children's stories as they fire the imagination, with a little wonder and also a little fear. I'm sure this has been the case right back into history - my own mother always remembers the line "we dare not go a-hunting for fear of little men" from Goblin Market, and gets a shiver just as she did when she was young.
What I do like is that JK Rowling has used not just the established mythological creatures but those from folklore, creatures like Boggarts, and possibly in danger of dying out as he only stories about them are passed on through word of mouth. Initially I was sceptical about this, but now I can see that some children after reading the books might want to go on and find out more - this is quite likely, as I wonder how many of
us went on to 'find out more' after reading Tolkien.
I have to say that her depiction of the employees of the Ministry of Magic is superb satire on civil servants, from the security guard taking the weighing of the wands to be the most serious of matters to the backstabbing and office politics.
