Hi Terry,
All four of the parks have plenty of activities for preschooler. The best place to see all the activities geared towards your daughter is the WDW
Preschooler page. From there you can learn about all the rides and entertainment for the little ones. You can also print out a map showing where just those activities are.
I will tell you that my three year old daughter's favorite park is Hollywood Studio. There is so much for her to do there. There is section of the park that is filled with Playhouse Disney attractions. There are meet and greets with characters such as JoJo and Goliath, the little Einsteins, and Handy Manny. There is a live show called
Playhouse Disney - Live on Stage. Even if your little ones hasn't watched any of the morning Disney Channel shows she will love the talking puppets and interactive elements of the show. She may also enjoy the live Little Mermaid and Beauty and the Beast shows.
If you are going to be there all day, consider stopping by Hollywood and Vine for either breakfast or lunch. It is a buffet style restaurant with characters from JoJo's Circus and the Little Einsteins. Again, even if your daughter is not familiar with the characters, I'm sure she will love it. Every 15 minutes two castmembers get all the little ones up dancing and singing. The restaurant is usually filled with kids under 7 all running around and having a blast.
Hollywood studios is definitely a place where kids can be kids. I think your whole family will enjoy a trip there.