Inside Hogwarts Castle is the most amazing theme park ride called Harry Potter and the Forbidden Journey. Incredible. Could be a bit scary for younger kids, but if they like roller coasters they'll have no problem.
There ate so many souvenirs and Potter world memorabilia to be had that your wallet could be hurting by the end of the day. Definitely sone things you can't find anywhere else. Dud I mention that the Butterbeer was awesome?
Something we did that I highly recommend is staying in one of the hotels inside the park. This gives you early access to the park attractions and gives you line skipping privileges at many of the rides.
Whew, I can't believe I just all that on my iPhone. My thumb's tired! Hope you enjoy the pictures (they're all iPhone as well) and I'll post again soon!