I have a little trick for you. For the girls, rather than buying fancy dresses for the cruise, pick up princess costumes. I hid them in my luggage and gave them to DD Sabrina one at a time when it was time to dress for dinner. Sometimes if we spotted a princess signing autographs we'd run to the cabin and do a quick change to match (cute photos). I'm not sure how many princesses we'll have on a Pixar Cruise... I bet there will be some.
One thing I always loved about fall cruises is there are lots of costume options available everywhere. There's a Wal-Mart (giant discount store) very close to
Disneyland (3.7 mi). There are also 2 K-Marts, both are just 2 miles from the park. If you'd rather shop near the ship, there are also a Kmart and a Wal-Mart not far from the cruise terminal (7 mi N, 7 mi NE).
It's amazing how a little girl dressed up as a princess acts like a little princess at the dinner table.
And I conversely have the photos to prove what happens when you dress a DD as a Pirate for dinner