Personally, I think that $100 is extremely generous.
In the past, we've gotten DS one of those twirly light toys, a balloon, a t-shirt or sweatshirt, and one toy (usually a med. stuffed character doll) on each trip -- so roughly $60. We also buy the occasional snack, but tend to pack a few snacks, juice boxes and candies with us too.
We don't stop in the stores at the parks -- we visit World of Disney at DTD toward the end of our trip. There's also a new store at DTD where everything is less than $10 -- maybe a good choice for kids who want to spend the last of their dough.
So, if you're looking for some place to trim your budget, I'd trim the kids' spending to $75. Let them know that they can keep any money they don't spend at WDW and you'll be helping them to prioritize their spending -- you may be shocked at how little a kid needs to spend at WDW if they can save the money for something they REALLY want back home, which may disappoint you somewhat, but is a great lesson in personal finance for the young!
Also, you mention $2000 spending money for the family. I'm assuming that includes all of your meal costs? If you're talking about $2000 for souvenirs and snacks, then that is much more than I budget. But I tend to be frugal. If you post with more information about what you plan to cover with "spending money", you may be able to get more advise about a good $$ amount.
One piece of advice that is off-topic from your original post: I highly recommend taking your kids to at least one Character Meal. It's such a treat and the kids get a kick eating while visiting with their favorite characters.
Enjoy your trip!
I think the $150 is an adequate amount. Our children save their birthday, Christmas, etc. money plus any extra they make along the way. It all depends on the child, however. Last trip our 2 boys (10 and 14) each had around $300 to spend. They both came home with around $175 left over. DD (16), on the other hand, brought $500 with her and had spent it all only half way through the trip. Our rule is, they can bring whatever they want and they can spend it on whatever they want, but when they run out, they run out. 
That system just seems to eliminate a lot of headaches for us. 
So instead of having $10 and spending that on something at the store right away, by the the time our trip comes around that $10 will have doubled maybe tripled it's amount. Then he would have more to spend on our Disney trip. He has a thick head like his dad. LOL!!
Wow! I've been lurking for about a year, now I have to add my 2 cents... I've taken the kids to Disney this way for a couple of years, and it works very well ... about 4 months or so before we go, I offer my kids a "match" on whatever money they can save from gifts, allowance, and extra jobs. This has turned my free spending guys into the thriftiest people I know! They work really hard to save and not spend for months, and with that money they feel real ownership. When they get their matched money they feel rich! They don't blow it on junk this way,(at least not as much ) It seems like when it's Mom and Dads money, they want everything, but when it's theirs, they end up coming home with money left over! (my 11y.o. ds saved $50 of his own, at 2.50 per week allowance, I matched that $50 for vacation, and he spent $16! ) The souvenirs they did pick are still their faves, because they had to think hard before choosing( big blue Stitch has to sleep with my little one every night now) 
