A 3 night can be very fun. But remember the ship will be crowded. I think this is what turns most people off on the shorter cruises.
Here area a few of my tips.
90 days prior to your cruise you can log onto your reservation and pick a Port arrival time (PAT). Pick the earliest one you can get. They start at 10:30 am. With a short cruise you will want to board as soon as possible to start the fun.
When you arrive at the cruise terminal you will be assigned a boarding #, this boarding # is tied to your PAT. They usually start boarding the ship 11:15-11:30.
I would have the kids wear their bathing suites under their clothes. That way they can take a quick swim before the pools get crowded.
You can grab lunch at the buffet restaurant on the pool deck Cabanas. Fill up your plate and grab a seat by the pool.
Pools- after the 1st day I suggest if the kids want to swim do it 1st thing in the morning or after dinner. Avoid the pools between 11 and 4:30.
during the pool busy times have the kids check out the kids clubs. Check for family activities going on. Or let the try out a fun game on the ship called Midship Detective Agency. It is a game that they search for clues throughout the ship.
Navigators - this is a newspaper you will receive each day that will list all the activities on the ship. It will tell you any family activities, game shows, movies. Here is a link that has old Navigators. the all the events may not be the same but this will give you an idea.
http://www.wdwinfo.com/wdwinfo/cruise-new/cr-stateroom-navigator.htm
Free Ice Cream- There is soft serve ice cream available on the pool deck. All you can eat.
Dinner- For some reason people love to line up long before the restaurants open. You have a reserved table. don't even get to the restaurant until your assigned time and you will be able to walk right to your table.
Elevators- if you are able use the stairs. the elevators are very crowded. Always avoid the mid ship elevators they are always busy.
Shows- Unless you want to sit in the very first few center seats you do not need to get to the show early. After the shows it is very crowded on the stairs and elevators. Walk to mid ship and take those stairs, or walk outside on deck 4 and by pass a lot of the crowds.
Room service- There is no extra charge for room service (you should tip a few $$) Let the kids order milk and cookies at bed time a fun treat.
Castaway Cay- There are plenty of chairs and umbrellas just keep moving down the beach until you find a good spot.
NOTE!- Everyone including children will need they room key card Key to the World Card (KTWK) every time you get off the ship.
You can have a wonderful time on a 3 day. It will hook you on cruising.