Our kids are 11 & 7 for this upcoming summer HHI trip. They LOVE it and have been going since they 2 & 6.
Although HHI can be really relaxed, you can also make it a go-go vacation too if you want. There are lots of activities at the resort to take advantage of plus the island is filled with lots of other adventures you can sign up to do. Nothing is very far away on the island. My kids like doing the Mickey tie-dye T's, as well as other arts n crafts such as pillow making, collage board, picture frames. They also have enjoyed and looked forward to the nature walks, marsh walks all lead by a Disney naturalist. And they always look forward to activities with B'Lou Crabbe and Shadow. We usually only do a few activities each trip b/c we love our beach time!! HHI has such a great sand beach that if perfect for making sand castles, forts etc. It also has great tide pools at low tide that all the kids on the beach love looking for sand dollars, starfish, fiddler crabs, hermit crabs etc... The ocean is also lovely with low waves and no riptides.
Then there is also so much to do off Disney property such as paddle boarding, kayaking, dolphin touring, dinner cruises, horse back riding, golfing, tennis, biking, boating, miniature golfing, shopping, nature preserve hiking. Literally if you really want a busy vacation, it's there if you want it...but its so nice you can also enjoy and relax if you just want to!!
My kids were talking about HHI on the way to school this morning, they soooo look forward to it every summer!!