The luau doesn't really have any elements that would appear to very young children, although there's nothing that would bother them, either. The first half of the show is something akin to a Disney Channel sitcom, while the second half features authentic dancing from various Pacific islands. I probably wouldn't bother to take my daughter to see it for her own benefit until she's at least 5 or 6 just because there's no characters or anything, but I wouldn't hesitate to take her if everyone else in my party wanted to go.
I don't want to "spoil" it, so I'll leave it at that, but if you have any specific questions, let me know.