No matter how much you learn online, nothing replaces a good guidebook you can hold in your hand and take on a trip with you. Having tips available on the spot can save you hours of hassle,or hundreds of dollars. And if you're exploring a new part of the world, background about history and culture can vastly enrich your trip.
This encyclopedia of WDW has so many tips, its worth its weight in gold. Although not specifically "For Kids", advice for family travelers abounds and all attractions are rated for appeal for different age groups. Other useful sections include detailed itineraries.
This book can help you make sense of the array of Caribbean family resorts available. Which island should you go to? Check "Island Report Cards", which covers friendly atmosphere, weather, new cultural experiences, transportation, and safety. If you're interested only in relaxing in one spot, head to "Best Places to Stay With Kids".
Covers Texas, Oklahoma, Arkansas, Louisiana, Mississippi, Alabama, Georgia, the Carolinas, Kentucky, West Virginia and Virginia-- and of course, Florida. What to See and Do, Where to Stay, and lots more.
"Unofficial Guides with Kids" are great guidebooks! This one covers fun places in Florida beyond Orlando. (Orlando, Walt Disney World, etc. is included too, though you'll probably want a guidebook specifically for WDW.) Especially good is the system of rating attractions, museums, etc., by age groups.
Here's a welcome trend: country-specific books for family travelers. Guidebook basics are covered, such as transportation, etc.; layered on top are fun suggestions for families. A nice extra is "Recommended Reading" for kids: picture books (about Leonardo, and so on) are a great way to enhance your kids' experience of Italy.
Another example of family travel books for specific destinations: brought to you by the budget-conscious Frommer's brand.