Basically the 5 major differences I would say are:
1) Size
2) Hotels
3) Transportation
4) Weather
5) Dining
1) At WDW the parks are more spread out (except DHS which is pretty compact). That means more walking in between attractions which could be tough with 3 kids. Plus to park hop at DLR it takes 2 minutes, but at WDW it could take up to an hour. There's way more entertainment options at WDW including an even larger DTD (with a Cirque du Soleil, Disneyquest indoor theme park/arcade, enormouse World of
Disney Store, Pleasure Island nightclubs, and tons of shops and restaurants), miniature and regular golf, water sports (water skiing, parasailing, jet ski), 2 water parks, and the list goes on. It's much easier to spend more time at WDW.
2) At DLR there are tons of very close cheap hotels or motels within walking distance from the parks. At WDW it is a huge advantage to stay onsite. Extra Magic Hours (EMH) allow onsite guests at WDW to enter a park an hour before and stay in a park (park changes every day) 3 hours later. Plus the dining plan at WDW saves money and is only available for purchase for onsite guests. Another perk to staying onsite is the use of their transportation
3) At DLR walking is everything. Walking from the hotels to the parks, or from park to park, or from DTD to the hotels/parks. At WDW the transportations system is much more complicated. From certain resorts you can take the monorail to a couple parks. Buses are the main way of transportation to everywhere. Boats are also thrown in there with the rest. And on top of that, you may want to think about renting a car because buses don't go from hotel to hotel. So if you stay at one hotel and want to visit another or eat a meal there, it might take a long time using WDW's transportation which would require a lot of transfers from bus to monorail to boat etc.
4) Weather is a huge difference. WDW is muggy and hot which drains you out quicker. Usually we don't take midday breaks at DLR, but at WDW we needed to, to refuel and get some rest. Also the rainy season in Florida is during the summer which is totally different from DLR's rainy season in the winter/spring.
5) Basically WDW has way more dining options and a dining plan that actually saves you money. Each park has a couple table service restaurants and character meals. Also some of the counter service places at WDW are actually quite good. Each WDW hotel (except value) have at least one table service place as well as a few counter service places and snack shops.