Hello, Fenella!
Epcot offers a nice assortment of rides for all ages and thrill levels, making it a great park for the entire family to enjoy. My daughter (age 6) especially enjoys The Seas With Nemo & Friends, Soarin', Journey Into the Imagination With Figment, and Spaceship Earth. You can see a
list of Epcot's attractions online, and filter the results to Age Interest, Thrill Level, Height, and more to help you plan your visit.
The
Kidcot Fun Stops around World Showcase are really fun to explore. Each of these locations are managed by Disney Cast Members from the represented countries, and teach children how to greet people in the native language. We purchased an Epcot World Showcase Passport kit for a small fee on a previous trip, and my daughter had such a great time taking it around and getting it stamped and written in as we traveled around the World Showcase. It's one of our favorite souvenirs!
My daughter also enjoys visiting with her Disney Princess friends around World Showcase. These lovely royals greet guests in their native lands, and from our experience, tend to have quick lines. Make sure to have an autograph book ready to collect signatures from your family's favorite princesses!
You mentioned that you are considering the Park Hopper Option for your Epcot day, and I would like to point out something to consider: The Park Hopper Option should count for all 4 days of your vacation, not just a single day. This could allow you some extra freedom to hop between parks during your 4-day vacation, even if you choose to not use it at Epcot. It is not necessary to purchase unless you are sure you will make use of it, but is a nice option to have if you like to be a little more spontaneous in your adventures.
I hope you enjoy a magical Walt Disney World vacation, Fenella!