I haven't been here for a while, but I just started to come back as we might be planning another trip. I have 4 year old twin boys and a 6 year old DS. We went to Disney once when the twins had just turned 2 years old and then again when they were 3.5 years old. My twins are a handful at home but they were terrific at Disney. We had our side by side twin stroller and that was the best way to keep them from wandering off. Sometimes we would park the stroller at one ride and then walk to another ride right after, in those cases I just naturally took charge of one of the twins and he would take the other and usually he would be in charge of our older DS too. We went at Christmas time and it was very busy and I think that made the kids a little nervous so they didn't try to wander off. We didn't necessarily dress the kids in the same t-shirt, but we did generally put all three in the same color so it was easier to remember what to look for when they moved. We really didn't get to do a lot of shopping because kids naturally want to get up and look around and it was just too hard to watch them. The only other time we had any trouble was on the tram from the parking lot and the monorail. Again, we went at the busiest time of the year and even if we were the first ones in line, people would just blow past us because we just couldn't move fast enough with the twin stroller, single stroller (these need to be closed up and carried onto the tram and monorail), three kids, back packs... If you are going at a slower time, it shouldn't be a problem. We found it easier to take the ferry across to the magic kingdom then to fight with people to get on the monorail. One day we were first in line and weren't able to get on three different monorails because people just flew past us. On the ferry you are able to keep the kids in the strollers and there is usually plenty of room. This is all I can think of for now. Good luck.
-Amy