That's a bummer!! My kids loved the water slides and would have been completely disappointed if they had been closed. When we were there last month, we got a notice under our door that for the next two days, the new infinity pool and grotto would be closed because they were filming something there. Turned out they were filming all over the water park area, which was a bit of a pain, but we made the best of it. I will say that the stairs to the slides were quite slippery, and I almost fell a couple of times. But it would have been nice if they could have just done part of the stairs and left part of it open for access to the slides. I'm sure there will be lots of unhappy people. If I were you, I would speak to management and let them know that your kids are disappointed, and see if there's anything they can do for you (free shave ice or something?). At least express that had they let you know earlier (assuming they knew), you would have used the slides more on your first couple of days. That was our frustration, too, that they didn't let us know much ahead of time, even though they had to have known about the film crews. That is something they could change.
I'm sure you'll still have a wonderful time!