Hi Erica,
Your 2 year-old can go on most of the rides. The only ones she would not be able to go on are:
At Epcot - Mission Space, Test Track, and Soarin'
At Hollywood Studios - The Tower of Terror and the Rock n' Roller coaster
At Animal Kingdom - The Kali River Rapids, Expedition Everest, Primeval Whirl, and Dinosaur
The vast majority of the rides and attractions at WDW can be enjoyed by children as young as 2 or even younger.
If you haven't seen WDW's special
Traveling with Little Ones at Disney Theme Parks web page, you should definitely check it out before your trip. You will find attraction height charts that will help as you plan your days at the parks and special maps highlighting attractions that are perfect for your pre-schooler. Your older children may even find that they are not tall enough for some attractions, like Animal Kingdom's Primeval Whirl.
Have a wonderful trip. Thanks for the question - Michelle