Hi Gareth,
I completely understand your feelings of wanting to make your family's vacation special. An illness of one member of the family affects everyone and its great to leave it all behind for awhile.
I so wish I had an insider secret for you but Guests are typically chosen at random to open parks or be in parades. There are times when they may have a celebrity VIP visiting the parks that they ask to be the Grand Marshall for the parades but usually its Guests that were lucky enough to be in the right place at the right time that were showered in pixie dust.
If you want to increase your chances of being selected I would plan to arrive at the turnstiles super early. Show your enthusiasm by wearing ears or matching shirts. Smile big and be talkative and friendly to the Cast Members. In other words, draw some attention (in a positive way) to yourselves.
In addition to a wonderful meal, here are some other special experiences that you may want to look into for your family:
*
Pirates and Pals Fireworks Voyage
*
Specialty Cruise to view the fireworks at the Magic Kingdom or IllumiNations at Epcot
*
Tomorrowland Terrace Fireworks Dessert Party
*
Horse Drawn Carriage Ride
Please feel free to visit us with any other questions. Its our pleasure to assist you.
I will keep my fingers crossed for you! Wishing you minnie magical memories :-) Allison