I've been doing the central MA to central FL drive since fall 2004, but my companions were college student (daughters) not 4 year olds, so my experiences may not all be helpful for you.
The first debate is I-95 versus the inland route. I've done both and will always choose I-95 over the inland route now given experiences on both.
How to break up the distance is the second debate. I will not drive 20-22 hours straight anymore, even with 2 or 3 drivers as there is a point where everyone in the car is tired as it can be hard to sleep on the road. It can be done by one person in two days if that one person is OK with driving 12 hours in a day.
My current favorite way to do it is to leave central MA after work between 5 and 6 pm and take I-90 to I-84 to I-91 to the Merritt Parkway to Westchester, NY. At this point I listen to 1010 WINS AM for traffic on the 1's to hear how NYC traffic is doing. If the traffic is good, I'll take the Cross Country Parkway to the Sawmill River parkway to the Henry Hudson bridge and down the west side highway to the GW bridge to the NJ Turnpike. If the traffic is slow, I'll take I-287 west over the Tappan Zee bridge and take the Garden State parkway until it hits the NJ Turnpike. THe only possible wrinkle on the NJT is construction (road widening) from exit 8 to exit 4 can slow the road down and cause backups. You can get off at exit 7 and take I-295 to avoid this if it's really bad, but you still have to endure the first bad stretch if it's backed up. Both roads take you over the Delaware River Bridge and back onto I-95 south through Delaware, Maryland, DC and Virginia (stay left at the I-495 beltway). I then stop in Fredericksburg, VA as there are plenty of hotels in the area (Fairfield Inn has good prices and free breakfast). This is about 475 miles and 7.5 to 8 hours of driving into the trip. It should be about 1 am when you arrive at your hotel. If you want to shorten day 1 a bit, you can find hotels just south of DC near Quantico and be off the road by midnight.
Day 2 I get up about 8 am and hit the road after a short breakfast period. From here you take I-95 to I-295 around Richmond to I-95 again. Figure on 1.5 hours to get to the NC border and then 3 hours each to get across NC and SC. Lots of places to stop here to stretch your legs and get gas and food. If you want to make this a 3 day trip, you can stop in the last few exits in SC and around Savannah, GA. If not, you continue across GA and and into FL. If you hit Jacksonville around rush hour, take I-295 around the city and save yourself anxiety and delays. Once back on I-95, continue on to the I-4 exit and then on to Disney. using my last itinerary as a guide, day 2 was 810 miles and 11.5 hours of driving. Ending point was Orleans Drive at Disney World.
You will definitely need an EZ Pass to get through tolls on this trip in a quick and efficient manner. Hope this helps. Driving is very much an option if you have time. You can reverse this trip and leave the Richmond, VA area after breakfast and get through DC after morning rush hour and NYC before evening rush hour. You may hit some traffic in CT though as it will be late afternoon when you hit the Stamford area.
