This book might be just the right thing to buy for your kids while they are waiting for the next Harry Potter book to be released. It has magic, and a weird plot, but it is full of innocence and good fun. I really think that "Which witch" will engage the attention of even the most active kid, and who knows, maybe even that of an adult who is tired to death of "serious things" and needs a respite.
The plot is simple. Arriman the Awful, a powerful evil wizard, has to marry. Unfortunately, he isn't in love, but he is all the same aware of the fact that he needs to have kids to prolong his legacy of terror. The solution Arriman finds is quite brilliant: he organizes a contest in evil witchcraft, the prize for the winner being his hand in marriage. Of course, the local witches are extremely happy with the news, and begin to prepare for the competition. One of them, Belladona, is in fact profoundly in love with Arriman, and would do almost anything to marry him. There is a little problem, though: Belladona is a white witch :)
I think that I have already given you enough details to have an idea of what this book is about. All in all, I believe that this book is excellent, and that your kids (and maybe you?) are highly likely to have enormous fun with the antics of Belladona and her friends in their struggle to turn her into a black witch. Read it, and enjoy!!