I don't think DLR has MyLittlePony stuff. WDW does, but I don't think it's at DLR.
Couple things I thought while reading the thread.
There are several kinds of light sabers at DLR. Cheapest are the Hasbro you can get at Target for 5-8 bucks vs 10 at Star Traders. Then there are $12 light-up, with-sound, mickey head themed, blue (only blue as of October) l'sabers. Then there are some spring-action ones, same as you can get at Target, for about $10 more than Target. And then there are the build your owns, which someone mentioned.
And if you do NOT want to deal with l'saber envy, then tell the kids that and rush them through the store. You can choose to NOT go through the store at the end of Buzz, but with Star Tours, you'll be going through the store.
Potato Heads...I bet if DS had someone to play with, he'd play with his PH. But for him,
Lego is more fun right now. He got some Star Wars parts from the place in DCA. The ONLY place now for the "fill a box" PH thing is EnginEars at DCA. They didn't have the top part of the Stormtrooper helmet, though, so that's a bit incomplete.
If they are all sharing, I would get them each a cheapie head (before you leave if they can play with PH while still there...have them ready at home if the souvenir is for after the trip), then see how many parts you can get in the BIG head container. Plenty of right/left arms combos! You want every kid to have proper arms. And the arms you buy away from Disney don't hold the Disney parts right, so you NEED Disney arms, right and left.
DS loves the spinners, but it sounds like you don't. I would recommend *bringing* the spinners you do have! We always bring old souvies back with us; reduces the "I wants" if he knows he already has something cool.
If you start pin buying, buy a set of locking backs for about 9 bucks. It comes with a tiny Allen wrench to put them on. Still not a guarantee that the pins will absolutely stay on, but it's better than the backs the pins come with!
The reason people buy "lots" of cheapie pins is because you can then trade people and some CMs for other disney pins (your pins have to be real disney pins...but buying them in a lot from ebay makes it cheaper), and it feels like a bargain (and often is).
I think that with that range of ages, you're not going to be able to buy one toy that they are all interested in and is *safe* for all of them. So maybe split it into 2 or 3 things?
The outlet, if it's like the outlets that move around the country, can sell hats. I think it might be worth a visit before your trip, if your kids might like getting their souvies done right away. Or maybe later on.
Oh, there are also little keychain type LED lightsabers for about $8. They are fun. DS has 3.

And another one (not exactly the same) from the Star Wars in Concert thing. I found a cheapie battery source, a seller on
amazon, which is good b/c those batteries (L13, or something like that) are spendy!