Hi Alicia,
Thanks for your kind words about the Disney Parks Moms Panel! We on the panel love helping you to plan magical vacations, and I am so glad that you are finding the thoughts here helpful.
Taking your 3-year-old daughter to Walt Disney World for the first time is going to be wonderful! I remember taking my daughter at that age, and the magic in her eyes was amazing. Be sure to stop by Guest Relations at any Disney theme park to pick up a free "first visit" button so that cast members and guests alike can welcome her for her first visit to the magic.
There is so much for a little one to do at Magic Kingdom. Some of my daughter's favorites when she was that age included Dumbo the Flying Elephant, "it's a small world," and Peter Pan's Flight, all located in Fantasyland. Some of the rides which are like transportation were also really fun for her, such as the Walt Disney World Railroad and Tomorrowland Transit Authority Peoplemover.
I am not sure of the abbreviation used for the second park you will visit, but I think you might mean Disney's Hollywood Studios. There are shows here that your little one may enjoy, including Disney Junior - Live on Stage as well as Beauty and the Beast - Live on Stage. There is also a great retelling of the story of the Little Mermaid in Voyage of the Little Mermaid; however, there is a very large Ursula puppet which might frighten little ones, so think about how your daughter will do with that before attending. Finally, consider making a reservation at
Disney Junior Play 'n Dine at Hollywood & Vine. This meal is fun for little ones and features Disney Junior characters singing and dancing.
I would love to help you plan more Alicia; however, I am limited in the amount of space that I have to answer.Please do let us know if you have any further questions!