Your family is going to have such a great time at the
Disneyland Resort this fall. With the Halloween decorations up and the holiday overlays to the Haunted Mansion and
"it's a small world" in full effect, October is a magical time to visit.
Now to answer your question, I think that the best place for your family to view
World of Color would be
Ariel's Grotto. The reason for this is weather. While it's usually pretty warm here, it does start to cool down in October. Nights can get quite chilly and breezy .Additionally, since water is a critical element of the attraction, you could get a decent amount of mist and moisture on you outdoors. For these reasons, I think it would be easier with a young child to have the seating advantage offered at Ariel's.
I just know that you are going to have a terrific time this autumn at the Happiest Place on Earth.