Hi Kayla'sMommy. My just-turned 8yo DS made his first trip to WDW when he was 2 1/2. I was really surprised at how much he enjoyed Epcot - Living Seas, The Land, Universe of Energy, SpaceshipEarth, Wonders of Life, and the boat rides in Mexico and Norway. AK wasn't open then, but I'm sure he would have just loved that, too. MGM probably had the fewest things for him, although he liked the HISTK playground, the Muppet Movie and the Ariel Show.
MK was a real hit, of course, and he enjoyed just about everything in Fantasyland (can't remember whether we avoided Snow White), Toontown, Jungle Cruise, Tom Sawyer's Island, Swiss Family Robinson Treehouse, Tomorrowland Transit Authority, Carrousel of Progress, the Walt Disney Railroad and the Tomorrowland Speedway. I think Dumbo held the record for "most rides" at six times over 2 or 3 days.
It took him a little while to warm up to the characters, so we made a PS for two character meals a little later in the week, which worked out well.
We were travelling with a large family group, and the parents of our 3 1/2 year old nephew made the mistake of taking their son on the Haunted Mansion first thing. He spent the rest of the vacation being reluctant to go on absolutely ANYTHING, which wasn't too much fun for them. By then he mistrusted each and every ride and attraction and asked incessantly "Is it dark?" "But is it DARK?" "Is it scary?" "Are you sure it isn't dark?". Normally he would be more of a risk-taker than our son, plus he was a year older, so I was glad we'd taken a more cautious approach, starting with tamer rides like Dumbo and It's a Small World to gain confidence.
Hope you have a terrific time with your DD!!