Hey one I know:
There is a Giant Sand Pit and activity area in the Dinosaur part of the Animal Kingdom. The kids can spend hours there and you might need to drag them away.
I’m not sure you could get 6 people in one of the cheap rooms however, but other than that, it certainly would be an option. Not just the cost of gas, but parking at the various parks is something like 10 bucks a day so there’s your break-even point right there.
Also if you’ll be doing meals at the parks, the Disney Dining Plan can be a good deal (only available to people staying on-site, I think). Though that depends on the age of the kids. My kids were just old enough last year that we had to pay adult rates for the dining, and they didn’t eat that much. For younger kids it’s probably closer to being cost-effective. I will point out that we ate 1 meal a day at the nicest restaurants that did “sit down” dining plan meals, and Typo and my meals wound up making up for the kids’ lack of eating, so I think all in all, we came out ahead.
If you do stay offsite as planned, ignore all of the above, obviously.
Stroller: I don’t know how much it would cost to rent them at Disney, but consider the hassle of getting the kids to and from the entrances to the parks. If they’re good about waling a little way while holding your hands, that’s an option. Your own stroller might make the airport portion of the trip a bit easier.
In Epcot, there’s a fountain in the pavement in the Future World area (near Mission Space, I think) that’s kind of like a big sprinkler the kids can run through. Maybe have them wear swimsuits under their clothes, and bring along a towel or two.
At the Magic Kingdom, there’s a playground called “Pooh’s Playful Spot” in Fantasyland and a small play area near Splash Mountain in Frontierland.
A quick note - When we went to WDW five years ago, we rented a house in Kissimmee. We were not much farther out than the Disney All Star resorts at the very southern end of the Disney property.
We were getting together with several other families, so the cost of the five bedroom house with a pool was divided up. I imagine there are condos or smaller houses available for rent also. As I recall, the rental house was much more economical than on-site hotels.
We did have to drive ourselves to the parks, and pay for parking. We could not participate in the meal plan. There are advantages to staying on site. You’ll have to figure out the trade-offs for 2008.
I have no advice, but you do have my sympathies. Disney World is (to me) among the worst places on earth. One of the reasons I try to be a good person is that I’m afraid that Hell will look like the Magic Kingdom…