Ahoy, Maria!
One of the best parts of a Disney Cruise is that you can always be celebrating, and it doesn't have to cost you anything! If you head to the Guest Services desk, they can give you a "Happy Birthday" button for your little man. If you note the celebration on your reservation, you might be surprised at dinner by your servers with a birthday cupcake or special dessert, as well as a resounding chorus of "Happy Birthday" by your servers and some of the nearby servers as well.
If you would like your stateroom to be decorated upon arrival, you can order the Birthday Celebration Package in the
Gifts and Amenities section on the Disney Cruise Line website. For around $52, you will get a birthday banner in the room, a Disney Cruise Line bed runner, a birthday card, and a large Happy Birthday magnet on your door. This will all be in your stateroom when you get there on your embarkation day.
You can also order a celebration cake, if you wish. These are also available to be ordered in the Gifts and Amenities section. Onboard the ship, you can purchase a special gift at Mickey's Mates or Treasure Ketch Retail Shops, both located on Deck 4 of the Disney Wonder.
I hope this helps with your cruise planning, and you are able to make your son's 6th birthday completely WONDERful!
Happy Cruising, Tracy V.