I think it depends on what you want to see and do. If you want to see all the shows at all the parks and ride all the rides at all the parks, then 3 days at UO and 2 at SW would be good.
But you have to decide which rides and shows are of interest to you and your family. Look at the websites or go to library and checkout books to see what is available at each park.
3 days would never be enough for us at UO, but some people think 1 day is more than enough. So you need to decide what rides and shows are of interest to your family, and take into account if you want to do rides more than once. If you "commando" thru parks vs if you "stop and smell the roses" thru them will make a difference.
Commando people doing limited rides and shows could probably do UO in one day and SW in one day. I just feel that traveling so far from home, I want to absorb it all and take my time and enjoy it all, so 3 days UO and 2 SW would be my suggestion.
And stay onsite at UO if you can. Early entry, express pass and not having to drive is the best. And the resorts are really beautiful with fun pools and good restaurants.
Hope you have a great time!