[Enchanted]

We're looking a good few years into the future but wondering whether it would be easy enough to do 2-3 days in Shanghai and then 5-6 days in Tokyo.
Was planning on going in May. Anything I should be aware of for weather/crowds?
Would I be doing Shanghai an injustice only visiting for Disney then leaving? We'll have two young children with us so main focus will be a theme park holiday. Although I'd also like to see a bit of Tokyo.

Are there are any other must sees/do in either place? Will I need to remortgage to go