I agree that most of the places on property sell things for about the same price. There is a place that I like to go to off property that has some good stuff..but you have to look at the tags to see if they actually say disney in order to make sure that they are actually disney ( if you care about that). One place next to the grocery store (publix I think)...it's close to orange lake time share properties. I can't think of the other.I know that wasn't extremely helpful but if I run I come across it in my paper work I'll let you know.
For us, the best thing turns out to be doing alot before we go. Then it doesn't really matter if the few things that we buy there are a bit pricey because we are not buying to much of it. For instance, I like to buy a watch with the year that we are there every trip. My daughter likes to get a twirley thing that lights up, and we all get t-shirts. But mostly everything else we bring.
Dollar tree has those glow in the dark bracelets and neckleses. They also have mini fans. One year we bought a small disney photo album from like wal-greens and took our polaroid camera. We then took a picture of the character and let them sign the bottom of the pic. This was awesome cause we had autograph and pic together. It was definately better than paying all that money for an autograph book at disney. Just be sure to use a sharpie to autograph with.
I believe there is also a number that you can call to oder stuff from the parks at home. I bet someone on this board knows it. If you get a few things here an there it won't be as expensive. Then put them in a box and only bring them out for disney trips. That way you start to collect useful things for the trips.
Also, your kids are at the age that they may enjoy making some of their own stuff like shirts, autograph books, photo albums, etc.
Good Luck,
Steph