The only time I ever went to Disney World I was in my 20's. Disney is fun, no matter what age! Enjoy your time with friends, and we'll watch for a post-adventure blog! :)
Must-do's? My list: Definitely take Thunder Mountain, and Finding Nemo Submarine Ride (formerly 2000 Leagues)! There's also the Haunted Mansion ride and the the Tiki Room. Of course, if they've seen the movies, they'll have to do the Pirates of the Caribbean ride. For viewing there's the Honey I Shrunk the Audience 3-D movie. I haven't seen that particular movie but if it's as good as the other ones, it'll be a great treat (and a chance to sit down for a bit). Enjoy!
When I was living in Redondo Beach, I would make 10 trips a year to Disneyland. We would have visitors come in from out of town. I would let them stay at our house and they would pay for me to go to Disney. I never grew tired of it. Now on the east coast, I have only been to Disneyworld about 10 times in almost 20 years. It is still a lot of fun.