Hi Carolina,
Welcome to the Disney Parks Moms Panel! It sounds like you are planning a fabulous trip to the Walt Disney World Resort!
With two girls who are 11-years old, I can honestly say that we enjoy all of the parks even though they are very different. If you can, I suggest that you visit all of the theme parks. Since we always visit all four theme parks when we vacation as a family, we spend at least five nights and get five-day base tickets that allow us to visit one park per day. We love Magic Kingdom, so we always visit it at least two days during our visit.
If you have to choose, I would prioritize the parks in this order, Magic Kingdom, Disney's Hollywood Studios, Disney's Animal Kingdom and Epcot. The choice is difficult for me, however, because at Epcot we adore Soarin' Around the World, Test Track and Mission: SPACE. At Disney's Animal Kingdom, Avatar - Flight of Passage is our new favorite ride and our girls always ride Expedition Everest - Legend of the Forbidden Mountain multiple times when we visit. If your family loves culinary experiences, you might want to prioritize Epcot over Disney's Animal Kingdom. The food selections throughout World Showcase are phenomenal.
Carolina, I also suggest that you check the attraction list for each park -
Magic Kingdom,
Disney's Hollywood Studios,
Disney's Animal Kingdom and
Epcot as you make your decision. If you do visit Disney's Hollywood Studios, be sure to take a walk through Andy's backyard in Toy Story Land and test your powers with the Force at Star Wars Launch Bay!
Magic, memories and Minnie Mouse hugs,
Donyell