Dear Sara,
Thanks for reaching out to us here at the Disney Parks Moms Panel with your question about the fireworks!
Cinderella's Royal Table is such a special themed dining experience and I am excited that you are going to try it out. The sound of the fireworks is muffled compared to outside, but if your son is extremely sensitive, I might suggest bringing noise-cancelling headgear (such as that worn by construction workers or others who work in high noise environments).
There are several times during the day when he might be startled by fireworks noise, but they are very brief.
Wishes, which are the main fireworks at the Magic Kingdom are at night, of course (times vary by season). It might be nice for you to watch those from elsewhere (may I recommend taking the
Resort monorail to the beach at
Disney's Polynesian Village Resort?) This will enable you to see the fireworks very well and to hear the music piped in, but not for him to be too disturbed by any loud noises.
Hope that you have a magical vacation!
-Jan K.