Welcome to Kissimmee I think you'll find it to be a very fun town with plenty of activities. Poincianahome posted some great link for you below.
As far as the job situation for your 18 year old, Disney usually always has jobs available. If you send him over to the Casting Center with is across the street from Downtown Disney they will let him know what they have open. Also, try the local hotels. They are usually have something avilalable as well.
As far as malls go, for work, I would try the Buena Vista outlets. They are always packed and if he's working on a commission than there's potential for him to make good money. They are located off 535 and I-4 where they intersect.
I wish you and your son the best of luck !