We did have a trip to just SW one year while visiting Orlando with small children but did go one night to
MNSSHP, so we got a little disney into the trip. If you had just the 2 and 4 year olds then I would say SW would be just fine but if you have a 9 year old, I think they are really going to want to go to WDW. SW does have happy harbor with a few rides that are great for your 2 and 4 year olds but the rest is shows etc. You could get the tickets that include Busch gardens and that would make your 9 year old happy. The problem with getting tickets for WDW for a few days for your entire family is that for only a few days the tickets are priced very high. As you add on days the price per day really goes down, per day. My suggestion would be to add on Busch gardens and acquatica and just do a SW adventure and do WDW another time. Have fun.