Ever since I've brought kids to WDW, I think one park per day is more than enough. If you are purchasing for the whole family, its a lot of extra money that you really do not need to spend. Travelling between parks eats up a lot of time and you really won't run out of things to do. I mean the only way I might consider it is if you really want to do a ride or two at HS and then go to Epcot.