That's an absolutely loaded question, because what's offensive is in the eye of the beholder. Basically, the comics on Celebrity "work clean" as they say in the trade, but there's still an occasional word that creeps in that might offend some young ears. Last cruise we were on the comic did one late night set that was clearly billed as "adults only." And even that was pretty tame. Other than the comics, there's not much to worry about, except that most kids won't understand or care for most of what's going on, unless there happens to be a magic act.
I believe the shows on Celebrity ships are "kid friendly". We had the "Ladder Guy" on our last cruise and he even brought a kid out of the audience and made him part of the show. It was hysterical. I really believe Celebrity is sensitive to their young cruisers!