I am a 12 year old and I think this is an awesome show, but I must advertise the cons.
NOTE: I have not watched this show on Cartoon Network, but I have seen these episodes online. The content specified in this review may have been censored, but this is something that needs to be known in case anything is not censored.
First of all, this is Dragon Ball Z, not Dragon Ball Z Kai. DBZ is the original Japanese version, which is inappropriate for a lot of reasons.
1. There is a character Master Roshi, who has a VERY sexual approach to the female characters. In one of the episodes, Roshi happen to fall out a ship that the Z fighters were riding in, and Android 18 happened to rescue him. He thanked her by grabbing her chest area, and plunging his face in them. There are countless other occasions, but it is common seeing him with O.O type eyes, if you know what I mean. He also has a very vulgar, suggestive ways of saying things that most tweens wouldn't understand.
2. The Devil Symbols. This MAJOR reason is something that I have gathered throughout the series. One is the fact that a character named Mr. Satan, would be present in the series. Analyzing his behavior will also give you clues to his bold name, such as his arrogance. He has a daughter name VIDEL (or DEVIL scrambled) who occasionally rides in a devilish car with Gohan. On the side of this "car", the symbol "666" can be found in a circle, with the name "SATAN" right above the symbol. Another symbol I have come across was the capsule corp. symbol. The future capsule corp symbol, with the Star in a Circle. Also some characters are named "Majin". Majin is a Japanese word, which translated to English is "devil". You may be beginning to categorize me as a radical, but this is very secretive and must be put out there.
3. Nudity. I have not gone deep into this category, but I have already seen enough that I have not expected. In some of the Dragon Ball Z movies, specifically, Dragon Ball Z: Bardock The Father of Goku, there are brief scenes of nudity. In one scene, there are babies in a crib on a Saiyan Ship, and these babies are unclothed and exposed genitals are shown. Also, and this is a scene in Dragon Ball, but since this is along the lines of Dragon Ball Z, I'll specify it anyway, Kid Goku is shown pulling is pants down and revealing his genitals. This was requested by a lady, who questionably asked him to do so. This is very explicit for a show, and I am not surprised that Cartoon Network let this show air.
4. Blood. There are many bloody scenes in the series, as it is based on Martial Arts and fighting.
This is my favorite show, when it is censored, because of the action and phenomenal storyline. Any other kid that watches this show might say this as well. Though due to this unexpected content, I have refrained from watching this, and I'm still weary about Dragon Ball Z Kai, on Nicktoons. Yes, 90% of this content is censored on Nicktoons, and I advise you to watch it. However, I DO NOT advise you to watch the MOVIES online. The TV episodes online are fine, but the MOVIES are not because they are the original Japanese versions. They have censored the bloody scenes, but the Devil Symbols are still present and some characters behavior is suggestive. You will know the difference between the movies and the TV episodes, because the movies have an ocean with a Japanese symbol at the very beginning, and the intro will say Dragon Ball Z, not Dragon Ball Z Kai. Also the original Japanese has older animation and visuals. I hope I did not confuse you in this review, and I hope this helped.