you will have a GREAT time whenever you take them!
we took our 3 (ggb) for the first time about 2 weeks after they turned 2. we also took the inlaws and my parents and it was so much fun. it took us the first 2 days to learn that the kids needed more down time (much better behavior once we started heading out of the parks after 2-3 hrs. in the AM and PM).
we then went when the kids were 2 1/2 (just the 5 of us), and it was an almost PERFECT vacation....it was so, so magical. i think this trip was easier because there was significantly less chaos with only the 2 of us calling the shots (we weren't trying to please 3 toddlers AND 4 other adults), and we stuck to their routine pretty well, and we brought the runabout stroller (which i LOVED using there),and
--most importantly--we stayed at the polynesian...this was FABULOUS for us!!!!super fast transportation when the kids needed to get home for nap/bed (no 40 min. bus/boat ride crankiness like first trip) and the runabout rolled right onto the monorail,and the beach was PERFECT for down time for the kids. they played on the beach every night for at least an hour before bedtime. plus, we watched the fireworks over the castle and then the electric water pageant and then put the kids right to bed (no hassles getting out of the parks).
we then took the kids back at 3, then 3 1/2, and we're going back a week after they turn 4!
each trip was wonderful in its own way. now that they are older and have more opinions, i am finding it more difficult to keep everyone content all the time , but i am finding age 3 more challenging than age 2, in general! i will also say that although they were close to being potty trained at home before our last trip, i let it slide completely while we were there , so i have yet to do the trip with 3 kids needing to find a bathroom IMMEDIATELY every 30 mins. (that truly might change my perception of how "easy" it is to do WDW with triplets!)
it is certainly not a relaxing vacation, but it is such a great time. i love planning vacations, so i spent loads of time preparing and i think that really helped us enjoy (and maximize) our time....my kids at 2 and 3 were good for about 2 -3 hrs. at a time in the parks, so i planned 2-4 activities/entertainments each morning and evening (after nap back at the hotel). after that, the things we did usually involved low-key activities (playing in fountains or playground area, snacking, exploring in a quiet area, etc) until it seemed like the kids were ready to leave the park.
have fun,