Upload & Sell: Off
You won't use the 85, too long.
I'd agree with this. The first day I put it on my camera one time, took 4 shots and decided it was too tight. Because of the crowds it can be hard to step back enough for that focal length to be useful. I still carried it every day because I love that lens and hoped to use it more but I it never left my bag.
I'm not overly concerned about weight - I'm pretty used to carrying a pack and given that most rides we are going to be going be rides that a 3 year old and 4 1/2 year old going on, I doubt I'll have to leave my pack, or worry about the pack getting wet. Sounds like the best option is to take a single body with the 24-70L and possibly a fast lens (my only option is the 85L) for those low light rides/places where flash isn't allowed. I'll take the 70-200L+ 2x converter for Magic Kingdom.
I have a Lowepro Pro Messenger 200AW and it fit my 5D3 with grip, 24-105, 35L, 85L, 70-200L, 2xTC, and 580EXII without being too cumbersome. It's small enough that it even fit at my feet on Big Thunder Mountain and in the bag pouch on rides like Dinosaur. With the waterproof cover I even took it on every water ride as well without issue. As an added plus it fits the 70-200 with body attached or the 70-200 w/ TC not attached to the body. You can put the 70-200 w/ TC attached to the body in but the flap will not close all the way.
If we do get delayed, it sounds like there are lockers available where i could store my tripod. Can someone confirm the lockers are large enough for a tripod
Most of the lockers are too small and the larger lockers fill up fast. I reluctantly left my $300 Giottos tripod in my stroller 20x a day without a problem. There were tons of strollers with bags left in them while people went on rides so I figure my chances were pretty good.
I hadn't really planned on going to Epcot (was only planning on going to Magic Kingdom and the Animal Kingdom Park. But given how much the kids like Nemo, sounds like it would be worthwhile to make the trip there as well. However, when I looked on the Disney website and it looked like the Nemo attraction is the only one that would be of interest to kids aged 3-4. is that assumption reasonable or is there something I'm missing
In the same building with Nemo is a live show with Crush, the turtle from Nemo. It's worth a see.
The Land pavilion (where Soarin' is) has a Lion King show (we didn't have time to see it though).
Over at Imagination is a kids ride with Figment and a fun musical play area after the ride is over.
Right next to Figment is Captain EO, the 3-D movie with Michael Jackson.
Spaceship Earth doesn't have a height requirement and your kids would probably enjoy it.
Also, Epcot has a the Epcot Character Spot where kids can meet Mickey and 3 other characters but waiting in one line. I think we waited for maybe 8 minutes.
Your kids are too small for Mission Space but there is a fun play area for kids of all sizes at the exit of the ride. You do not need to go on the ride to play in it.
Innoventions East and West are basically large educational play areas with different exhibits for kids. There is a "ride" (calling it a ride is a bit of an overstatement) with a large articulating arm that your older kid might be tall enough to ride.
There is next to nothing for kids ages 3-4 in the World Showcase. It would be hard to fill up an entire day there but you could easily fill 3-5 hours.