Common Sense Media is off the mark with their rating. Big Brother is appropriate for tweens and up, and I only say this because most children under 12 I believe would not fully grasp the main concept of the series. The host of Big Brother, Julie Chen, has coined the show as being family-friendly. Also, it deserves more than just two stars.
Big Brother has an interesting premise in that 15-16 contestants move into a house where they are under constant surveillance, with cameras and microphones capturing their every move and every word. Indeed, it is a voyeuristic series. What makes the show so enticing and engaging is that the contestants compete against one another in weekly challenges to gain power, safety, luxuries, and rewards. Not to mention, viewers can impact the game throughout the season by taking part in voting and polls. At the end of the week, the contestants themselves decide who is evicted (or eliminated) from the house (Think Survivor but in a house setting, basically). The last person standing in the house after the intense, 3-month power struggle wins the half-million dollar prize.
Regarding the content of the series, "showmances" and romances are part of nearly every season of Big Brother. There are scenes of playful flirting and kissing, and rarely do two contestants go all the way (Fully censored if it does happen, and very brief. Can hear them making out, can see sheets moving -- all in night vision). In every season there is at least one gay contestant. Sometimes there is discussion about sexuality and intercourse. Occasionally the contestants will have access to wine and other forms of alcohol, and some houseguests smoke.
Furthermore, there is a lot of swearing in the show. The typical swear words are bleeped, and recurrent insults such as "idiot," "moron," "bitch," and the like are audible. As in any reality show, the contestants engage in heated arguments and fights, whether for personal reasons or gameplay. In one season, a contestant was removed from the show for head-butting another. Of course, there are a number of controversial contestants who enter the house each season. During Big Brother's 15th season, at least four contestants consistently made crude and derogatory racial, homophobic, and misogynistic remarks towards other houseguests or otherwise, but these people in question were fired from their jobs upon being evicted, due to their inappropriate behavior.
Do not expect to find any good role models or positive messages in this show. In the Diary Room and in their introduction videos, the contestants admit that they will be fine with lying, cheating, stealing, back-stabbing, and trash-talking if it gets them closer to the $500,000. Some houseguests are willing to manipulate others and play with their emotions, form fake relationships, and go against their own friends and allies. However, many of them do admit that they are only engaging in such behavior strictly for game purposes. There are one or two contestants each season that try to play the game with honesty and integrity which is refreshing to see.
My only major gripe about Big Brother is that the casting is predictable and they often cast the same types of people and stereotypes each season, although I commend them for choosing contestants from different age groups.
Also, it is important to keep in mind that seeing as Big Brother is 24/7, there are live feeds online and Big Brother: After Dark spin-off show which are completely uncensored and uncut, and allow viewers to take a look inside the house whenever they want. This is what the children need to avoid. Make sure to stick to the broadcasted show on CBS. If you can find the Canadian version of Big Brother, it is equally as good, and the content is more or less the same as well.