We drive down, too, from just west of Nashville. I'd rather have the short flight with a three year old and baby, but it's twice as expensive as driving, and I'd rather have that money for souvenirs.
We're changing the drive up a bit this year. Leaving two days early, driving halfway, spending the day at PCB, driving another 3ish hours, spending the night, driving to Clearwater, spending the day, then heading to WDW to check in that night.
Driving gives us the freedom to spends those two days at the beach, plus head to IOA for a day in he middle of our trip. We're hoping that by doing most of our traveling at night, the kids will sleep most of the trip.