You know your son best, and at 11, he IS likely to think of Pooh as a kiddie ride, but not necessarily Peter Pan.
Overall, WDW attractions aren't thrill rides; they are storytelling rides with great details. Many thrill rides are little more than a box on a metal track. The only reason to ride them is the thrill of the intense movement. Disney rides are far more immersive. If either of you is expecting to find intense-motion rides, you might be disappointed.
It is especially worth adding that Epcot doesn't even have many rides. Much of what Epcot offers is non-ride attractions.
I can't say enough, the thing that makes WDW special is the attention to detail. While Fastpasses are great, and long lines are boring, the WDW queues are often quite entertaining themselves. Most of them are designed to set the stage. the Haunted Mansion queue is especially full of stuff to do/play with.
Splash isn't quite as wet as it once was. If you are unlucky, you might end up getting some water on your hair(do), Avoid wearing thick denim at WDW in June, especially on any rides with water. Generally though, if it is 80-sih, you'll won't get very wet on Splash, and you'll dry off within a few minutes. (Kali Rapids is a different matter; about 1/4th the folks who ride Kali end up VERY wet. There are also several VERY wet rides at Universal's Islands of Adventure.)
As others have said, afternoons get HOT. They are also pretty crowded. Even though you only have one day in each park, try to find a way to escape the peak afternoon heat each day. Aim to use ALL your after-dark park hours. From MK, it is pretty easy to take the resort monorail over to any of the 3 monorail resorts. They are fun to see, and GF has an especially enjoyable lobby with plenty of seating, shops and music. All have food, gift shops, and arcades.
For Epcot, the China, France and Canada movies offer a respite. The Mexico indoor area is also cool and fun to explore. All the WS pavilions also have Kidcot stations, but only a few are indoors. At each country they'll stamp it, and he can color for a bit if he wants. At 11, I know he's a little beyond the coloring age, but both of you can still enjoy the respite from the heat.
Another way to escape afternoon heat is a long meal/snack somewhere indoors. If possible, eat lunch after 1:30 or dinner before 5:30pm, or even just take an indoors snack break to escape the heat. The MK Little Mermaid ride and Dumbo play area are also afternoon respite options.
In AK, we linger in the bigger gift shops. The new eatery and gift shop in Pandora is a good places to relax. The animal exhibits aren't indoors, but they have shade. It Is Tough to Be a Bug will get you out of the heat for a little while.
Indoor character queues are another option, though you'll have to stand.