I have done it once...but that was w/ no kids. we made it to the Atlanta area and then went on from there for the 2nd day.
My DH and I have debated driving to WDW again...but w/ 4 kids all younger than yours eek.
Beyond just the driving consider the fact if you are doing this in conjuction w/ SB (it does get crowded down there) if you leave Sat after kids are out of school and leave at say 5 am...you will not tour the parks when you arrive...and possibly if you split it into 2 days so consider that on the return too. figure if you drive Sat-Sun both in and out you'll have Monday-Friday for touring
that can be enough for some, we weren't willing to give up touring for driving and saving some money plus I wanted the kids to have a rest day at home before school resumed.
(I went SB last week March in '09 but we pulled kids from school Thurs-Friday and came home the following Friday)
the drive...
portable DVD's more than 1 may help.
lots of fruit, crackers in the car for snacks and water.
any handheld games you can think of electronic or otherwise.
Pack a filling lunch and stop at a nice rest area say Tennessee and take an hour break to rest, and stretch out.
Good luck w/ whatever you decide
You can do it...I have down long car trips twice w/ a nursing baby (once to Myrtle Beach SC and to Atlanta)