Keep in mind that there is a big difference between Disneyland (in California) and Walt Disney World (in Florida). Disneyland is the original, but it is much, much smaller, with 2 parks. I haven't been there yet but am dying to go. I'm actually thinking "Hmm... when I travel to China, maybe I can add a day at Disneyland Hong Kong to the beginning of the trip..." :LOL
I go to WDW in Florida every year for a week - I'm a graphic designer, and WDW is my creativity recharger. I love it, and can't wait to share it with my kids! It NEEDS several days, because it is 4 MAJOR big parks, 2 waterparks, several golf courses, 2 minigolf courses, a sports complex, a shopping/dining complex, a nightclub complex and many beautifully themed resorts. It's around 45 square miles!!! I absolutely LOVE WDW, but it has to be done right. If you choose to go, plan ahead and read up on what is there - Magic Kingdom is like Disneyland (but a bit more spread out, I think), Disney Studios is focused on movies and Hollywood, Animal Kingdom has attractions and live animals (with some of the most beautiful, spacious habitats I've ever seen - everything is carefully themed), and Epcot has two sections, future world (focused on communication, technology, the sea, agriculture, space) and World Showcase featuring pavilions of many countries with people who actually are FROM those countries working and performing there. I think there is a lot of educational opportunity in Epcot and Animal Kingdom especially. Go in the off season. Be at the parks when they open in the morning (lines are short then), use Fastpass, and take an afternoon break to recharge - come back in the evening - WDW is especially magical at night. Consider exploring the resorts - rent a boat, go for a walk, go horseback riding, ride a surrey bike. In the past 5 years I've never waited more than 20 minutes for ANYTHING at WDW, usually less than 10 minutes for rides. It can be done! (What CAN'T be done is seeing everything in one trip. That's where people tend to stress themselves out.)
Yes, the characters are everywhere (and fun to meet and get autographs from, btw), the food is expensive (although they are working hard to offer more healthy choices), and there are tons of gift shops. With prior planning (and limits set on buying) it can be a great vacation!
The original reason Disneyland was built in the first place was because Walt wanted to provide a clean, friendly, wholesome, safe place where families could have fun TOGETHER, because he disliked sitting on the sidelines watching his daughters ride rides at fairs and such, that he couldn't get on with them. (Yes I know, it's become a money maker and marketing opportunity - but it is still much nicer, cleaner and friendlier than any other park I've been to!) All the rides at Disney parks are such that parents can ride WITH their kids. Where else can you snorkel with sharks, eat authentic food from several countries, see a Japanese drum performance and a celtic rock band, ride in a simulated mission to space, wander through a botanical garden, see how food might be grown in a space colony, learn how movies are made, see amazing live shows, ride a well-themed roller coaster or two, see rhinos and giraffes just feet from you, see an incredible fireworks show, awesome parades and Cirque de Soleil all in the same day? (Ok, so you'd need more than a day, but you get the idea!)
Your kids won't be missing out on a critical part of childhood or anything if you don't take them, and if they want to go as adults it will still be there. But if you plan ahead so you can do it in a relaxed way, follow your kids lead and most importantly let YOURSELF be a kid for a while, you'll probably have a great time! (I'm going in November, but am ready to leave NOW!)
The Unofficial Guide to WDW is really, really great, and I've found the Passporter guide to WDW helpful as well. Passporter.com also has message boards with people who can help you with just about any question. (The Passporter authors recently had a baby, and seem to be AP parents as well!) Allearsnet.com is the most complete website I've seen about WDW, including sections about dietary restrictions, special needs, a stroller FAQ, and taking kids of different ages. And I love to talk about WDW, too! (Obviously, based on the novel I just wrote.