Hello Jennifer,
On behalf of all of us here on the Disney Parks Moms Panel, I'd like to wish your son a happy and magical fifth birthday! He is going to have the time of his life and it is sure to be a trip to remember for the rest of his life.
While I love both Disney's Animal Kingdom and Disney's Hollywood Studios, I think he might enjoy Disney's Animal Kingdom more at his age. Don't get me wrong, Disney's Hollywood Studios has some awesome attractions and shows. However, in my experience with my kids, at that age, they have really enjoyed Disney's Animal Kingdom more.
He is sure to like Kilimanjaro Safaris, Kali River Rapids (as long as he meets the minimum height requirement), Rafiki's Planet Watch with the Affection Section, among many others.. The Boneyard over at Dinoland, USA is a great spot for him to run off some energy and "dig" for dinosaur bones while you take a break and sit. Some of the greatest shows are there, too, like Finding Nemo - The Musical and The Festival of the Lion King. Lastly, on our last family trip there, my then 6 year old enjoyed the
Wilderness Explorers. This is a self-paced interactive activity throughout the park and it happened to be her absolute favorite thing of her entire trip! I was amazed by how much she learned (and I did, too) while having a blast doing it. This also offered a great distraction for her while her older brother rode on some of the rides that she wasn't tall enough for. So, if you or your significant other wanted to ride one of those attractions, your son and the other parent could enjoy this activity without him feeling left out.
Have a magical visit creating lots of treasured memories. Your trip will be here before you can say "supercalifragilisticexpialidocious!"
~Allison L