Hi, Tina! Let me start by saying that the
Candlelight Processional is one of my favorite holiday traditions at Disney World. It is so beautifully narrated and the music is amazing.
That said, I have only experienced it without my kids! While I think my 10 year old daughter would enjoy it, I know my 7 year old son would be asking "How much longer?" about 10 minutes into the 40 minute show. You know your son best, but I think it might be a bit long for your little mouseketeer.
Instead of waiting in line for a seat, how about enjoying it from the sidewalk behind the pavilion? This will eliminate the wait time in line, and if your son gets fussy, you can have some freedom of movement or leave if necessary.
I know it will not have the same effect as if you were sitting inside the pavilion, but perhaps in a few years this will be something you will be able to enjoy together as a family. Whatever you decide, wishing you a wonderful holiday season in Walt Disney World!