Just a few specific suggestions:
*Autograph Books and Pens
*Beanie-Baby Plush (smallest size plush characters.)
*Candy Wand (a plastic tinkerbell wand filled with star candy)
*Glow Merchandise (A variety of spinning light up toys featuring Mickey Mouse, Buzz Lightyear, Winnie the Pooh or Tinker Bell)
*Epcot Passports (if you are planning a visit to Epcot-- children can collect different 'stamps' at KIDCOT stations in the World Showcase.)
*Pal Mickey (A more expensive gift at $60. It is a small interactive plush Mickey that acts as a tour guide through the parks offering information about attractions, shows and character meet and greets. He also tells and jokes and plays games)
*Magical Moments Pins (Pins that light up during certain attractions and parades within the parks, indicating a magical moment. They also play games.)
*Starter Pin Trading Lanyard (comes in a few varieties featuring Mickey and Minnie, The Disney Princesses, or Toy Story Characters. The package includes a pin trading lanyard and a couple of pins. Pin trading has become very popular in the parks and your children will have the opportunity to trade with Cast Members and other guests)
*Mickey Mouse Ears (They can be embroidered with your children's names.)
*Guest of Honor Badges (A red name tag similar in shape to Cast Member nametags engraved with your child's name. Guests who wear the badges are often addressed by name by Disney Face Characters and Cast Members)
There are plenty of other great ideas, but I thought some specific suggestions might help.
Have a magical vacation!