We took our son last year 2 weeks before his second birthday. We fit the trip in on the end of another trip because we wanted to get him there before he turned two for selfish reasons - he was free until he was two and I was 7 months pregnant, and wanted to go before the doctor told me I couldn't. We got up in the morning and drove the hour and a half from where we had been staying and got to the park around 11am. It was a monday, so it wasn't too busy yet. We paid the extra few dollars to park in the preferred parking (which I highly suggest!) and went in. My son was actually a bit afraid of the actual rides...he didn't like the carousel and freaked out on this large blow up jumping mat. My husband was annoyed and that we had paid all that money to get in and my son hated it and kept saying that he was too young. We got B to calm down and got him in his swimsuit. He had a great time in the water - the play areas, slides, lazy river. We even got off the lazy river and walked right up and watched the parade. He was very happy with just playing in the water and we didn't push any more rides on him...he seemed to be having lots of fun.
There are a lot of shows you can go see and restaurants to eat at and fun giftshops. We ate dinner in the one restaurant and then visited the gift shop and then headed home. We actually didn't say overnight there, and drove straight back to Pittsburgh that same night (I know! but we needed to get back!). We even stopped at the Lancaster outlets on our way home. We were fine with going just the one day, and can't imagine spending multiple days there, but a friend of mine did go for two days and they really enjoyed it. There are a lot of hotels in the general area that looked fine.
We didn't do a character meal because our son was going through a faze where he was apprehensive of large characters - so we decided to skip it. I heard that it is lots of fun but you need to plan ahead and make sure you book early to get the meal that you want.
The other thing I would suggest would be to make sure everyone (and by everyone I mean even mom and dad) have watersocks. It was so hot that day and the pavement was almost unbearable to walk on. We had my son in watersocks, but we didn't have anything to wear on our feet, and both my husband and I wished we had our own watersocks. I had flipflops, but they would fall off in the water and I would have to store them before the lazy river...it would have just been easier to have watersocks.
We also did take the stroller in with us and were glad that we did. I was able to bring water and suntan lotion and change of clothes easily, and B was able to rest if he needed to.
Overall we had a great time and will go back when our second child is old enough to enjoy it. Make sure you look for coupons before you go! Have a great time!