We walked right in to Philharmagic last week. However, the parks were not very crowded. I'm pretty sure it has FP though.
I definately agree that this is by far the calmest of the 3-D shows. There is nothing in the movie that is meant to scare you. It is totally unlike ITTBAB and HISTA in that respect. It is more of a surprise factor.
We all thought it was absolutely wonderful. However, only you will know if your little one will be bothered by the 3D effects, wind and water. By the time we got to HISTA my sons knew to look for the place the water came out. One of them put his foot over it so it wouldn't squirt him. You could probably do something similar if you are worried that the small water spray might bother your toddler.