Hi Tracy,
What an absolute perfect place to celebrate your big 5-0! If you have not done so yet, be sure to register
here for your birthday celebration at Disney World. Disney wants to help you celebrate your special day by offering you free admission to one park on your birthday. What a great gift!
Ok there is no official way on how to be selected to be in any of the Disney World parades. The best advice I can give is luck, timing and lots of pixie dust. Select Cast Members are always on the lookout for guests to join in on the parade fun. They are looking for families just like yours, having a wonderful time at Disney. We were selected one time to join in at Hollywood Studios Motorcar parade and at the time we were selected, we were standing in line for Playhouse Disney. We had struck up a nice conversation with the Cast Member while we waited for the show. Many laughs and minutes later, she left only to return with another Cast Member who asked us if we would like to be a part of the parade. What a treat!
Occasionally the parade marshalls are special guests of Disney World, for example a Make a Wish family or perhaps a celebrity visitor, but usually they are families that the Cast Members found simply enjoying the magic and in the right place at the right time. You can certainly ask at the guest relations counter, but I would be sure to do it immediately upon your arrival to the park. This most likely will not work but it never hurts to ask. Be sure to wear your birthday button proudly, smile big and say please--you never know! Good luck!