I'd wait until both of your kids are old enough to be able to handle, at the very least, a lot of walking before you bite the bullet on a WDW trip.
If DLR is at all a hassle with your four year old...magnify that many times at WDW with its larger parks, much more complicated logistics for everything and the corresponding need to not only plan but plan with contingencies and be willing to adapt if need be (FP, dining, characters, you name it; one day we got to Typhoon Lagoon at opening, only for them to announce it wouldn't open for the day, so we had to hightail it to Blizzard Beach), and brutal summer humidity that'll bring out the worst in your family and the others around you if you/they aren't used to it.
WDW is many things, but relaxing, casual, or low key it is not.