I've directed the show before and Snarker sums it up well. In addition to the parody of Busby Berkeley, there's some broad humor that any age kid can enjoy. There are a few mild double entendres in "Pensacola", but I doubt even the brightest 14-year-old would get them.
"Singapore Sue" is a parody of a specific song: Jimmy Cagney's "Shanghai Lil" in FOOTLIGHT PARADE. IIRC the "yellow-face" is kept to a minimum, if used at all. But I have to admit I wouldn't accept a SHOWBOAT Queenie in blackface just because the original did it that way. So it will be interesting to see what they do with the number. If one finds it objectionable, I think 9 and 14 are old enough to discuss issues of representation.