Hi Steph,
Walt Disney World is a great place to celebrate a birthday, especially a notable one. There are lots of activities that could make this a special birthday, but since you mentioned animals, let me suggest the
Wild Africa Trek at Animal Kingdom as a possibility.
Several of my Moms Panel friends and I did the trek together in September and it was a blast. Knowledgeable, fun guides take you behind the scenes at the Kilimanjaro Safari, giving you an up-close view of hippos and crocodiles. You'll walk over a swinging bridge above the crocs (can't believe I really did that!) and get a tour of the savannah in a special vehicle. Then, you stop and eat a delicious lunch at a pavilion overlooking the savannah. We watched the giraffes, including a baby, the whole time we were eating.
The guides also take great professional photographs of you and your party, which are included in the price of the three-hour experience.
I highly recommend the Wild Africa Trek. I'm terrified of heights (and so was one of my friends), but we were very proud of ourselves for conquering our fears on the bridge and want to do it again with our families.
The link I provided above gives more details and the restrictions that apply. I think this might be just what you are looking for.
Please let me know if I can answer any other questions for you as you make your plans. Enjoy your birthday celebration with your family!
Wilma