There are 4 differnt grand gathering events. I have done them all several times and they are pricey, but have been worth it. The rule is that you have to be on property to book these events and at least 8 members of your party have to go. The first is the Good Morning Gathering at Tony's Town Square in the Magic Kingdom The cost is 11.99 for children and 24.99 for adults. It is a character breakfast and is only for parties of 8 or more. The characters include Chip, Dale, Tony, Minnie, Goofy, pLuto and a visit with Mickey at the end.
The second is the Safari Celebration at Animal Kingdom. The price is 19.99 for children and 59.99 for adults. You meet at the Bird Show and then they wlk you to the safari. It is after the park is closed so there is no one else and some photo ops of the empty park! You take the same safari ride but without the "show". It is also very slowed down and they tell you a lot of things about how the park was built, etc. After the safari you go to Tusker House for Family style dinner and some entertainment with musicians. There are also a couple of characters (they change who) and some opportunities to touch/see up close some small animals like a giant spider.
The third is the Msagical Fireworks Voyage out of the Contemporary. The cost is 14.99 for kids and 32.99 for adults. You meet out by the dock (if it is raining you meet inside) where they have a huge dessert buffet for you. While you are there Captain Hook and Mr. Smee show up. You get plenty of time with them. There are then two other pirates that come and the whole group (not yours) is divided into two boats. The pirates take you out into the Lagoon and you first see the electric water parade. They are singing and dancing with you to entertain during the wait. They also ask lots of trivia espescially around the Pirates of the Carribean Movie. They give little prizes to the kids for that. Then you get a great view of Wishes with the music piped in. It is far away but you can see everything. At the end they take you back to the dock where Peter Pan is waiting for you. Again, he spends plenty of time with you. I always get to the end of the line though so I can take as many pics as I want!
The final Grand Gathering event is the International Dinner and Illuminations Viewing at Epcot. You meet at the old Horizons building and they have a dinner with a lot of different cuisine from around the world. They also have chicken strips for the pickier eaters. There is a show while you eat and at the end Minnie and Goofy come out and dance with all of the kids. It is really fun! There are also lots of desserts here! You are then escorted to a private viewing spot for Illuminations. The cost for this was 19.99 and 59.99
All of these include a pin about the event. These prices were from last year so they may have changed. They seem expensive but many include dinner and they all have the free pin. Plus it is an opportunity to do something really differrent. The character time and shows are much better than anywhere else. You spend more time than even at a regular character meal because the participation is limited. You can also buy Grand Gathering T-Shirts online at the Disneyworld site. Hope this helps.
We have 16 going in June, from 1yo - 62yo. We're doing the GG Fireworks Voyage, and a dinner at 50s PT, and a dinner (buffet) at Chef Mickey's. A small group of us (4) are doing a lunch at CRT. I'm hoping ALL is fun! 
