Even before I read Banksy's reply above, I was going to say Florida too.
People may think it is a bit corny but the weather is wonderful (outside tornado season!), the kids and Mrs will love it and you will end up enjoying it yourself too.
The theme parks, and water parks are exceptionally clean and well run and everybody are happy wherever you go.
It will set you back a few grand but if you think of it as a once in a life time holiday, it is well worth the cost (so much so that I've actually done it three times now!).
There's other great stuff to do away from the theme parks such as Daytona (if you like motor racing), Cape Canaveral (if you like space ships), the beaches (you can sail with dolphins if you like) plus NBA Baskett Ball -Orlando Magic, NFL Football - Tampa Bay Buccaneers, NHL Ice Hockey - Tampa Bay Lightening and NBA Baseball Tampa Bay Rays all within a couple of hours drive away.
There's even the Tampa Bay Rowdies if you wanted to watch a proper footy match!
To be honest even with all that lot the kids and Mrs still just wanted to stay in Disney and the other parks.
The highlight of the lot was swimming with Dolphins - everybody loved that.
As I say it is quite expensive but well worth it imo.