Did you see James Patterson's Op/Ed piece on cnn.com? It's called, "How to get your kid to be a fanatic reader." It's definitely worth reading http://www.cnn.com/2011/09/28/opinion/patterson-kids-reading/index.html?hpt=op_t1
His main point is that the more kids read (no matter what they are reading) the better readers they are! So if your kid loves Captain Underpants or Junie B. Jones or the Guinness Book of World Records or The Vampire Diaries, but doesn't want to read the classics, it's okay. They are still improving their vocabulary and becoming better readers.
Patterson has a website - ReadKiddoRead - with lots of great book recommendations. Check it out and help your child find a book that he or she will not want to put down. I will be looking it over to find new books to add to our library collection.