Hello Julie,
Thanks for stopping by planDisney with your question. You are in for an amazing experience! I recently got to experience my own twin nieces' first trip to Walt Disney World, and seeing the parks through their eyes was magical. You are going to create memories that will last a lifetime.
In order to enter each park, you'll need to have a
valid admission and park reservation for each day. All of the reservations are made separately, so if you want to go to
Disney's Hollywood Studios on one day while your brother and niece head to a different park, just make sure your reservation is for the park you want to go to. You all could even plan to meet up for a midday break back at your resort to swim or even get together in the evening for dinner, either in
Disney Springs, on
Disney's BoardWalk, or at one of the Walt Disney World Resort Hotels.
If you do decide to go to Disney's Hollywood Studios together, there are plenty of fun things for a four year old to experience.
For the First Time in Forever: A Frozen Sing-Along Celebration,
Toy Story Mania!, and
Mickey and Minnie's Runaway Railway are a few of my favorites. Plus, for attractions like
The Twilight Zone Tower of Terror and
Rock 'n' Roller Coaster Starring Aerosmith, you can always take advantage of
Rider Switch. You would go on a ride while your brother hangs out with your niece, then he gets to ride without spending extra time waiting in line.
If this is your niece's first trip to Walt Disney World, be sure to stop by Guest Relations at any of the parks and pick up a First Visit button for her to wear.
Hope this helps. Have a magical vacation!
Diane