We recently visited Fantasy Surf in Kissimmee, which is an indoor surf simulator, it's about $25 per adult for 30 minutues and great fun. You have two types of surfing that you can try, body boarding which is pretty straight forward to pick up and actual surfing using a very small board which is very tricky to do but with some practice I am sure it is easy as demonstrated by my instructors.
I would recommend that only people over about 13 try this as when you fall over it's not as soft as it looks so may be a bit painful for small kids but if you like a good work out and don't mind the odd fall I highly recommend it, although I found the actual surfing pretty tough!!!
Fantasy Surf is conveniently located off of Poinciana Boulevard between SR 535 and Hwy 192, for more information and directions please visit there web site.