Note: This is a review of the Funimation English dub version of this series.

Violence / Gore:
This show is very clean. Maybe an angry outburst, but not much else.

Nudity / Sexual Content:
Very rare in this show. Some of the outfits are more skin-tight than others, but they are on stage in spandex so it's just being true-to-life in that aspect. One character (female) is overly fond of another character (also female) but she is not necessarily portraying romantic feelings.

Potentially problematic theological themes:
If there were, I don't remember them. This show is mostly about the stage productions that are put on.

Other potentially problematic themes:
Maybe a mild swear. A couple characters drink a little (i.e. while talking in a restaurant).

* Kaleido Star is a lovely anime about a girl who just wants to try her best. Sora dreams of being on the Kaleido Stage, doing gymnastic performances that make people happy. On her road to stardom she hits pitfalls and hardships, and finds out that not everyone is as pure in their love of the stage as she is. I found myself rooting for Sora as she persevered - all the while still being true to herself. She experiences personal growth and encourages those she meets. Honestly a wonderful series to watch. My only complaints were that the episodes don't always have a lot going on, and the constant stage drama can get a little tiresome.
I recommend this series to people who enjoyed Princess TuTu - though PTT has a little more going on in it.