What PPs have said is all good advice, here's what I can add (my most recent trip to the world included my just over three year-old nephew and his 16 mo twin brothers).
1. Take it slow and easy. There is so much for them to take in ... you will be amazed at what grabs their interest - just go with it! And keep the camera handy.
2. Stroller is a must. Not sure what model you have, but my sister has the the double one available from Orlando
Stroller rentals and it is fantastic. (Compact for a double, nice comfy-shaded seats, etc.) We thought the 3yo would be ok without his own stroller, but after day 1, we ended up renting one for him each park day. The heat and excitement was too much. That said, it's nice to have the stroller outisde the parks too.
3. The walk from BLT to the MK entrance is about 10 mins tops (at a leisurely pace) - this can be faster than the monorail and will likely be much quieter if the little ones have fallen asleep in the stroller.
4. Take the time to introduce the kids to the characters before you go - especially if you plan to do character meets or meals. (In small doses, Playhouse Disney - oops, I guess it's now Disney Jr - is a great way to do that.) When we were planning our last trip, the not quite 3 yo loved looking at the DisneyWorld magazine we got from the
travel agency. It was a great way to explain some of what we would see and do. We also looked up some rides on
youtube with the 3yo. (Turns out that he really really really wanted to try Soarin' .... he just made the height cutoff and LOVED it)
5. Expose your twins to restaurants near home - it will help you figure out how to plan your meals on vacation. We regularly eat out with my sisters family, so the boys are used to restaurants. This was great b/c we were able to do the Dining Plan and used the TS meals as "not so obvious" downtime. That said, the boys aren't morning people, so we ordered from gardengrocer.com and ate breakfast in our BLT villa most mornings. (We did do one breakfast buffet a Chef Mickey's.)
6. If the kids have never flown before, maybe get them a story about airports and planes (I DON'T recommend Robert Munsch's Angela's Airplanes for this purpose). We got a neat book at Chapters that had flaps etc. that takes you step by step from checking in to going through security, to stowing your bags to landing - the twins really liked it and so did the 3 yo. You might also want to take the kids out to an airport beforehand if possible - just so they can get a feel for it.
7. Make sure to pack some small favourite toys/stuffed animals for the kids to play with during downtime in the resort. The 3yo's stuffed koala came almost everywhere with us on our last trip (we ended up calling him the fourth kid, but that's another story.) Also pack some new, inexpensive toys for the airplane. You might want to pack earplugs and (sugarless) suckers as well.
Ok, I'm gonna stop now .... sorry for the long post!
