I loved this movie. My nine year old really liked it and was totally engaged. My 6 almost 7 year old was a little restless toward the end (it's a little over 2 hours long). We discussed the fact that it is an entirely African American cast (my 6 year old finally noticed this toward the end). We also talked about Michael Jackson and that Lena Horne was mixed.
Both kid reviews on this site expressed being offended at the part where the dancers were "naked" and "the guys and girls where taking there clothes off". This was around 1:46 into the movie. The dancers took off their huge over costumes in a scene where they were setting themselves free since the witch was dead (sprinkler system, she's allergic). The women ended up wearing what amounted to a bikini, and the men wore slightly more than a jockstrap. The dancing was in no way suggestive or sexy, just a Broadway-style, musical, corps-type dance number. So I let my children watch it, my finger on the fast forward button just in case. They were not disturbed by it in the least (they are very sheltered), neither was I.
All in all, a great movie with some historical significance. I highly recommend it.