I would do Epcot and here's why.
I have kids the same age as you, and your 4-year old will probably be too small for the best rides, Flight of passage and Expedition Everest, both of which are 44 inches minimum. They are also to small for Primeaval Whirl (48 inches) but that is pretty unpopular. They are probably both tall enough for Dinosaur (40 inches) but it is terrifying for that age group, and Kali River (38 inches) but that is such a short ride (and you'll get soaked) so it is kind of a one and done thing in my opinion. That means really what you will be doing are Kilimanjaro Safaris, Navi River, maybe Kali River, and going to the shows/walking around the zoo trails. That is nice, but that is an easy one-day itinerary. Frankly, Animal Kingdom is always a half day for us (we don't really care for the evening show, and it is always so hot there).
In contrast, at Epcot there are three height-restricted rides, but they are only 40 inches so your kids would probably be tall enough (Mission Space, Test Track, and Soarin), and all of those rides are great fun. There is also the Seas pavilion with the Nemo ride and Turtle talk with crush and a big interactive playspace and aquarium, Spaceship Earth, Frozen Ever After, Gran Fiesta Tour, Living with the Land, and the Figment ride, none of which have any height restrictions. Also, you have the entire World Showcase to explore, which is both absolutely beautiful, but also educational. My 6-year olds LOVE exploring the different countries, finding a souvenir in the shops, and snacking on gelato or caramel corn or any of the other goodies there, and listening to an outdoor concert. You could easily spend one day in Future World and one day in World Showcase, or two days with a mix of both. Epcot also has our favorite restaurants of any park.