There is no way I would book this meal on a Party night For kids, unless they really want to meet the Beast, the Castle is the Castle. It is the same for Breakfast , Lunch and Dinner.
I know you have a BOG ADR for breakfast I think. I would keep that one and skip dinner. I would get to the park at 4:00 and have an early CS meal, and be ready at 7:00 when the party starts. There is nothing worse than anticipating how wonderful someting is going to be, building it into your plans, and then hearing "Can we leave now?" I did that when I booked the Princess Tea for my DGD and me to enjoy together. It was an expensive event, and one that I had built up in my own mind as something my precious Kady would love. She did not. It was really difficult not to be upset with her, but she was not the one who wanted this. I did. I said it was for her, but it was really for me. Over $225 later, and several hours of watching a pickle puss endure her tea, we left. SHe was as gracious as a 5YO could possible be when she really wanted to be back at the resort swimming with the rest of the family, but lesson learned for this Nana.