How old are the birthday boys/girls?
I love the idea of Disney/birthday tshirts, but of course, a 15 year old might just roll his/her eyes at the idea.
The character meal is a great idea, too. Again, based on your kids! Mine (boy, now 6) would go bananas to get a birthday wish from Mickey and the gang! We're big fans of the character meals at Tusker House in Animal Kingdom - we've had great interactions there in the past, and the food is good.
If you're the kind of family that enjoys a nice sit-down meal (we are, we rarely eat quick service), you can order a cake for your birthday kids when you check in for a dining reservation. Or you can order it in advance and have it personalized.
You can do a special activity with them - or send them off to do a special activity on their own. (Again, I don't know their ages, so I'm not sure whether this applies.) Our family did the Pirate & Pals Fireworks Cruise a few years back, and it was loads of fun. It starts at the Contemporary with a little reception hour - snacks and drinks and mingling and a chance to meet & greet with Captain Hook & Mr Smee. Then you're led to your "pirate ship" for the evening - a pontoon boat on the lagoon? You have a pirate guide who cracks jokes and gets the crowd laughing as the boat heads out on the lagoon to the fireworks viewing area. When you're in the right spot, they kill the motor, and you float there while watching the fireworks over Magic Kingdom. They pipe in the same music through the boat so you can hear it all in time with the fireworks. It's pretty cool. Then it's more silliness from your pirate guide while you return to the dock, where a "surprise" character is waiting to welcome you back to land. We took my son (now 6) when he was 3 1/2, and he still repeats some of the jokes the pirate guide cracked, and he still talks about his experience with the surprise character at the end. The fireworks, while not immediately overhead, were really cool seen from that perspective. The whole experience was loads of fun.
And, if they're the right ages (between 4 and 12), there's a kids-only pirate adventure that they can go on. The pirate adventure leaves from the marina at I think 4 different resorts - I know the Yacht Club and Caribbean Beach Resort are two, not certain about the others. We had my son, then 5 1/2, do the one from the Yacht Club. We brought him to the marina, he was fitted with a pirate life vest, and the handful of kids going that day were led aboard a pontoon boat "pirate ship" to start a sort of scavenger hunt for pirate treasure. There was adequate supervision for the kids, as a few Disney cast members were also on board to keep them safe and entertained. They apparently sailed around the lake, stopping at various points to "discover" a clue, and finally found the hidden pirate treasure, which was then brought triumphantly back to the Yacht Club docks. The kids were given a snack aboard the boat, too. When they got back, the "treasure" (little toys and candies, if I recall) were shared among the treasure hunters. My son was bubbling over with excitement, and he still talks about "when I was looking for pirate booty" more than a year later.
Beyond that - what would your birthday kids like? Do they trade pins? Is there a character'd they particularly love to meet? Bibbidi-Bobbidi Boutique? Pirates League? A special meal location? I can speak from my own experience, but I have no idea what your family would like best!
My biggest recommendation to nearly every Disney-goer would be to purchase the Memory Maker package. (Bought a week in advance of your trip, I think it's $150?) You'll get access to all photos taken of your family by photopass photographers (at character meals/meet & greets, out and about in the parks, plus on rides). For us, stopping briefly at many of the photographers we pass is just part of the vacation. Sure, not all the photographers are top-notch, but we've had some absolutely priceless shots taken by Disney Photopass photographers, and a few have really gone above and beyond to help us make - as well as capture - a memory. A week vacation typically nets us about 200-300 photos and magic shots. And the best part is, I'm in the pictures with my husband and son. That NEVER happens otherwise. The Memory Maker/photopass photos are worth every penny to us. But again, everyone's got their own take on things - YMMV!
