Hi Lauren,
Your 13 year old will definitely enjoy Epcot for many reasons. However, I want to reassure you that toddlers and preschoolers will find it to be a wonderful Park as well.
I highly recommend that you head to
The Seas with Nemo and Friends Pavilion. The slow moving, mesmerizing ride, ends in a multi-level aquarium. The children can enjoy seeing dolphin, sharks, manatee and countless brightly colored fish. Don't miss
Turtle Talk with Crush. My youngest daughters could spend hours in this Pavilion alone (and we have). ;)
Another fun place to explore with younger children at Epcot is the
Imagination Pavilion. This ride also ends in an interactive area. There are "squares" on the floor that when the kids jump on them, it'll make the noise on the photo. For example, jump on a photo of an elephant and it'll trumpet like one. I have lots of great photos of my girls enjoying these.
You could entertain the younger children at these attractions while your 13 year old heads over to
Soarin' in The Land.
Hope this gives your some ideas. Please send me a follow-up question if I can help you further,
Kaylene