Hi Elizabeth,
Your question was cut off a bit, so please feel free to send over another question if I don't answer yours fully.
I definitely recommend taking advantage of the FastPass+ system to make reservations for later in the afternoon. Crowds are typically at their largest in the late afternoon, so making the reservations is a good way to be able to experience the more popular attractions. If you are staying on property, you can make FastPass+ reservations 60 days in advance. Otherwise, you can make them 30 days in advance.
Before your FastPass+ window opens, I'd recommend checking out all of the attractions at Epcot online so you have a plan of what you want to experience. Be sure to check the height requirements so you'll know what your 4-year old is able to go on. At that age, my kids really liked Soarin' (your 4-year old may be too small though), Journey Into Imagination With Figment, Finding Nemo, and the Gran Fiesta Tour in Mexico. If you plan to eat at a table service restaurant, I'd also recommend making Advance Dining Reservations so you'll get your preferred time and location.
I hope that helps! Have a great vacation!