The single adult means you'll be limited to rides where the 7 m/o can go.
The only one I can think of that 4 yo might like but not sure if 7 m/o can go is Soarin'. You'll have to check on that one and see what you think.
I would get some relaxed mileage out of (in no particular order):
- Living With the Land
- Spaceship Earth
- The Seas w/ Nemo & Friends
- Maybe Turtle Talk w/ Crush -- everyone says it's awesome, we keep missing it
- Journey into Imagination w/ Figment
Even though not all of those rides are high on every adult list, they should all be entertaining for your kids
Also, I would make heavy use of the various pavilions which generally have interactive activities, you can spend as long or as short as you like:
- Spaceship Earth exits to an area with games etc., many of them will easily keep your 4 yo entertained for a while in a relaxed environment. If very crowded and lines for everything, maybe not, but we usually are fine.
- Mission Space (which you won't ride) exits into an area that you can also reach through the gift shop -- there is a crawl & climb playground & a large cooperative video game for older folks. Your 7 m/o might appreciate a chance to crawl in the tunnels a bit (escorted by 4 yo) if it's not too crowded and 7 m/o is very mobile. If happy in stroller or being held without a lot of crawl time, you can skip this.
- The Seas pavilion has an aquarium atmosphere
- The (Imageworks) pavilion after Journey into Imagination has good stuff for 4 yo, and some that 7 m/o might be able to do as well with assistance
- Opinions vary wildly on Innoventions. You just won't know until you take a peek inside
That's way more stuff than you're going to get done, but those are the things I would look at / focus on when making a plan.
Also, you don't say when you're going but if the weather is at all amenable I would put the kids in quick-dry / bathing suits / rash guards, there are a couple of splash & play zones. One is on the walkway between Future World & the World Showcase, and I forget where the other one is but I know it exists. They can have some fun splashing around for a while, especially in the time after Future World closes and before Illuminations they can be a great place to hang out and have some fun.