I have to say that I'm just amazed at the amounts that seem "normal" in this thread. I guess we bear off the "mean parents" palm in more ways that one, but the most I would allow my child to spend in souvenirs &/or extra snacks would be $25 per trip at the outside. Anything spent is their own money; we don't give out money for this purpose.
It appears that we are unusual, but with few exceptions we actively discourage the purchase of souvenirs while travelling. For one thing, it is just more to pack. Mostly, our reasoning is that travel should not be a glorified shopping trip. We travel quite often (including about 4X/yr in Orlando) and for us, the point is to acquire memories and experiences, not stuff. If we bought home things from every place we go, we would need a second house!
My DS has a WDW/Universal souvenir collection, arranged in a special shelf box: park maps. While he does have a couple of toys, etc., that were purchased in Orlando, what he really treasures is the maps. Every single one for every single trip he has ever taken. He takes them out and looks at selected ones at least once a week. "Hey, Mom; remember this one? That was the time that I was finally big enough for Splash!" The collection is priceless, but it didn't cost him a dime. (He also keeps road maps and tourism brochures from other places.)
I'm not condemning spending money at WDW; we own stock, so by all means, feel free! I just wanted to point out that it is also OK to *not* give your kids a lot of spending money, (even if you have it), or to stop them from spending their own under these circumstances.