Hi, Michael!
Oh, absolutely! You can definitely show up at the
Walt Disney Theater in shorts and t-shirts. You'll see
every sort of attire at the live shows and throughout the ship. There may be couples coming from Palo or Remy in their cruise finest to families who opted for quick-service dining by the pools -- and everything in between.
Although the Disney Dream is a huge ship, you're still only a few decks away from your stateroom at any point to change if you so desire. Our family is constantly doing quick changes throughout a Disney cruise -- that's what makes staying organized in your stateroom so important. In fact, my boys will often dress up for dinner (as required by Mom), and then run back to our staterooms afterward to get comfortable. My big kids will watch the live show with the family but then dash to the teen clubs with their newly-found friends on board. Therefore, they
have to be in shorts and tees!
I recently answered a question for a guest who was concerned about others in her group opting out of the formal/semi-formal night, and I explained the various options to her
here. Maybe this answer will help you plan your family's cruise, too.
I hope I've cleared things up for you, and please let me know if I can be of further service. Have a wonderful day and a magical vacation.
Bon voyage,
Andi