My kids are 10, 8, 5, and 3. We love the rides.. besides Soarin and Test Track, everyone loved Spaceship Earth, Living with the Land, the whole Imagination pavilion, everything in the Seas (be sure to see Turtle Talk and the rest of the exhibits). They liked Innoventions, especially the fire game. Club Cool is a big hit, too.
In World Showcase, the Mexico boat ride is their absolute favorite. But Maelstrom is great, too. There are lots of characters to meet. My kids liked looking around in China, Morocco, and the Japan the best. Trying out new sweets is a big hit. The trains in Germany! The little one loved those. They liked the bands in UK and Canada, and my little guy had a great time dancing for the Mariachi band.
We did a few of the Agent P missions, but it was hard for them to all hear/see on one phone. They were really cute, though.
Epcot is definitely entertaining for the under 10 set, its just not as obvious as MK.