I think the parts that my two enjoy the most are the countries (although both could and would ride TT as many times as possible - youngest was 8 last trip). This is a scary sounding ride, it took awhile to convince him to ride it the first time, because it sounded more scary than he was in the mood for. However, once he rode, he wanted to get right back on! Maybe prepare the 7yo for the noise being scary but explain the ride in detail (maybe ride it alone first if you haven't been on it before).
We try to catch as many of the performances as possible - the acrobats in China, the juggler in France, Off Kilter in Canada, etc.
If they haven't done the mask or passport, they should try this! Even if they have done it before, each visit is a whole new experience!
Oh! The candy lady in Japan--big, big hit!
The boat ride in Mexico.
The various types of foods - try something they haven't had - maybe the Japanese pavilion with the chef cooking right in front of you?
We also enjoy Living Seas--can spend a while here looking at the fish--Nemo's friends! Also, we have eaten at Coral Reef, which is an entertainment in and of itself!
Great character meetings also! They are more hidden than other parks--you may have to ask someone to direct you there! We have had great interactions there!
Also, if you haven't done the Storybook Breakfast at Epcot I would suggest that as a great way to start the morning for 3 girls (even my two ds's loved this!).
We love Epcot, but it is a park a lot of adults with children don't bother learning about...very unfortunate in my opinion!