Hi Danielle,
The
Whispering Canyon Cafe is a great family restaurant. Be sure to let the Cast Member know that you are celebrating a birthday. If you are not staying at the Wilderness Lodge, a very memorable way to get to the restaurant is by boat from the Magic Kingdom.
You can have a personalized custom cake made and waiting at the restaurant. Just call the Cake Hotline at (407) 827-2253 at least 48 hours in advance.
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When at the restaurant, be sure to have your child ask for a bottle of ketchup. Also, I recommend asking for a large drink of some kind; if you don't get a large, insist (politely) that they bring you one. If you are really up for some mischief, wear a shirt from another Orlando area theme park to dinner! Once a three foot tall wooden chef joined our table for the rest of the meal, because my youngest spilled his chocolate milk. However, I don't recommend having an accident just to get the chef.
Just remember that every Cast Member is different. They all want you to have a good time, but some are more out-going and interactive than others.
Some other celebration ideas can be found
here.
Have a magical vacation!