I wouldn’t worry at all about them having fun. They will. Our kids are older now (14, 11, 11), but we spent two days at Epcot with all three around age 4 and 7, continuing once a year as they have aged. Epcot has always been their second favorite park, even at that young age. We even took the oldest at 2 by himself. You just never know what they will enjoy.
Our plan at Epcot was always to pick what we enjoy. Our kids didn’t put a lot of emphasis on “rides” vs “experiences” at that age. We would stop for music or entertainment, wander through shops, eat and drink, and ride the ride at Mexico. But other than that, they just tagged along and loved it. When they got older, we did the agent P thing. And now, they could spend an hour in the Japan store looking at Pokémon and anime. I say just plan what you want and they will have fun too.