Hi, Christi! You are asking this question to a panel of moms who all have been bringing their kids to Disney since before the kids could walk! While they might not remember every detail of their vacation, you will certainly cherish the memories!
While your 5 year old will have to skip some of the "big" rides like Expedition Everest and Rock 'n' Roller Coaster, there are so many wonderful attractions he will enjoy! You probably won't even be able to do everything he wants to do.
Some things to do that come highly recommend from my in-house expert, my 6 year old son! In Hollywood Studios, he enjoys meeting the Power Rangers, riding Toy Story Mania, The Great Movie Ride, Honey I Shrunk the Kids Movie Set (a play area), eating at Pizza Planet, and MuppetVistion 4-D.
In Magic Kingdom, his first stop is always Buzz Lightyear Space Ranger Spin. Other favorites include Peter Pan's Flight, Flying Dumbo's, Aladdin's Flying Carpets, it's a small world, and Goofy's Barnstormer.
To get a better idea of what will be available for your son, click
HERE for a list of Height Requirements, then click
HERE for a list of all the attractions (you can filter this list by park, child's age, height, however you want.)
Have fun researching Disney World!