We also like to do different things when going to Florida; we stayed at St Augustine (St George Inn - Excellent) for four nights during our last trip and are booked in for another four this August.
We stopped off at Daytona Beach on the way there which broke the journey up nicely. Plenty to do for the kids (5 year old was happy all the time, after a couple of days 15 year old would rather have been in Orlando!), nice beaches, sight seeing tours on the local trolley etc.
Both kids enjoyed the "ghost" tour in particular and its also a very interesting city to walk around. It is more for adults than children but you should have no problems keeping them happy for a short stay or a day trip. We enjoyed it because its so relaxing and makes a pleasant change from non stop Orlando. There are many interesting restaurants which are only a short drive away, the type that you wont necessarily find in Orlando.
Cheers Michael