So imho I think the epcot of today, and even the 80's epcot, is more geared for older kids, teens and adults than for younger kids. I love Epcot and my kids have enjoyed it more as they're now teens but they still feel like it's light on attractions. Just not enough rides!! I love Epcot for what it is but I agree that MK reigns supreme for the youngest of kids.
Right now, If I was taking littles to WDW now, I'd peg DHS as the second best park for preschoolers with all the shows like Beauty and The Beast and Frozen sing along, TSM, SDD, Alien Swirling Saucers, Disney Junior meet/greet, the dance party, Muppet Vision, lightening mcqueen, Star Tours and MMRR.