My kids' first trip together, they were 2 and 4. They both agreed that Epcot was and still is our favorite park! They absolutely loved it so much! My son would ask to go into the big "golf ball" several times!
My husband and I just had a nice time strolling around, enjoying the snacks and drinks, and the kids had a ball making the little masks (we loved doing them at the Kidcot Fun Stops - now they have Duffy but we loved the masks) - they also liked seeing the things like candy sold from other countries.
They spent hours at the living seas too! I had to drag them out of there.
They also used to find really fun things to do at Innoventions all the time. There's a fire safety house where the kids learn about fire safety, and my DD still likes to do it (it's really designed for toddlers to really young kids, but she doesn't want to grow up!).
We still go to Epcot almost every day when we to to Disney!