I went with The Unofficial Guide to Walt Disney World. I found it to be good but in the end didn't need it as I realized that all of the information they provided was either here on these boards, on the Disney website, etc. That said, if you have never been it may provide you with information that you might not think to look for, and therefore it may be more valuable for people going for the first time. I did find it well organized and enjoyable and easy to read.
Try the Complete Walt Disney World and Universal books by Mike and Julie Neal. I have most editions of their book and learn something new each time. They are incredibly detailed and have great color photos.
I like Birnbaum's Walt Disney World for Kids. It is meant to be enjoyed by kids and used for planning so there are lots of color photos, maps, graphics. I bought it for my preschool grandkids who don' yet read but they will enjoy seeing pictures of all the rides and having sections read to them. It would be perfect for 7-12 year olds. It has a scrapbook and autograph section at the back.
I recommend a Hidden Mickey book. Not planning really, but a fun activity to do everywhere on property. You might consider checking your library for Disney travel books before investing in one. I found the info online to be more helpful and up-to-date. https://smile.amazon.com/Hidden-Mic...&qid=1498512180&sr=1-1&keywords=hidden+mickey